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Entrance Exam Information dan repost
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Ifa Boru Boarding School dan repost
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BBO - Hagayya 16/2018 Ministeerri Barnootaa Itoophiyaa Qabxii Qormaata Biyyoolessaa Kutaa 12ffaa Bara 2018 Ifoomse.
Haaluma kanaan, bara 2018, akka waliigalaatti barattoonni 550,201 qormaata Kutaa 12ffaa fudhatan.
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FDRE Special Boarding Schools dan repost
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-----------
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Remedial Exam dan repost
19: For the equilibrium: Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq) (blood-red color), adding solid KSCN will: 
A) Decrease the intensity of the red color 
B) Increase the intensity of the red color 
C) Not change the color 
D) First decrease then increase the color 
Answer: B 
Explanation: Adding SCN⁻ (from KSCN) increases reactant concentration. By Le Chatelier, equilibrium shifts right to form more FeSCN²⁺ (red complex), intensifying the color.

20: The reaction quotient Q is used to: 
A) Calculate the rate of reaction 
B) Determine the direction a reaction must proceed to reach equilibrium 
C) Find the activation energy 
D) Measure the enthalpy change 
Answer: B 
Explanation: Comparing Q to K indicates direction: if Q < K, reaction proceeds forward; if Q > K, reverse; if Q = K, at equilibrium.

21: Which statement about dynamic equilibrium is FALSE? 
A) Macroscopic properties remain constant 
B) Microscopic processes continue in both directions 
C) The equilibrium can only be approached from the reactant side 
D) The ratio of product to reactant concentrations is constant at a given temperature 
Answer: C 
Explanation: Equilibrium can be approached from either reactants or products side; the same equilibrium state is reached regardless of starting point (at constant T).

22: For the reaction: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), Kc = 4.0 at a certain temperature. If equal moles of CO and H₂O are initially present, what fraction of CO is converted at equilibrium? 
A) 1/3 
B) 1/2 
C) 2/3 
D) 3/4 
Answer: C 
Explanation: Let initial [CO] = [H₂O] = a, and x = amount reacted. At equilibrium: [CO] = [H₂O] = a-x; [CO₂] = [H₂] = x. Kc = (x·x)/((a-x)(a-x)) = x²/(a-x)² = 4. So x/(a-x) = 2 (taking positive root) → x = 2a - 2x → 3x = 2a → x/a = 2/3. Thus, fraction converted = 2/3.

23: Adding an inert gas at constant volume to an equilibrium mixture of gases will: 
A) Shift equilibrium toward more moles of gas 
B) Shift equilibrium toward fewer moles of gas 
C) Not shift the equilibrium position 
D) Always increase the reaction rate 
Answer: C 
Explanation: At constant volume, adding inert gas increases total pressure but does not change partial pressures or concentrations of reactants/products, so no shift occurs.

24: Which change will increase the value of Kc for an exothermic reaction? 
A) Increasing temperature 
B) Decreasing temperature 
C) Adding a catalyst 
D) Increasing reactant concentration 
Answer: B 
Explanation: For exothermic reactions (ΔH < 0), decreasing temperature favors the forward reaction, increasing Kc. Kc changes only with temperature.

25: In the equilibrium: 2NO₂(g) (brown) ⇌ N₂O₄(g) (colorless) ΔH < 0, cooling the mixture will: 
A) Make the color darker brown 
B) Make the color lighter or colorless 
C) Not change the color 
D) First darken then lighten 
Answer: B 
Explanation: The forward reaction is exothermic. Cooling favors the forward reaction (Le Chatelier), producing more colorless N₂O₄, so the brown color fades.

26: For a reaction with Δn = -1 (change in moles of gas), if Kc = 10 at 300 K, what is Kp? (R = 0.0821 L·atm·mol⁻¹·K⁻¹) 
A) Kp = 10 
B) Kp = 10 × (0.0821 × 300)⁻¹ 
C) Kp = 10 × (0.0821 × 300) 
D) Kp = 10 / (0.0821 × 300)² 
Answer: B 
Explanation: Kp = Kc(RT)^Δn. Δn = -1, so Kp = Kc / (RT) = 10 / (0.0821 × 300). Option B expresses this correctly.

27: Which industrial process does NOT rely on manipulating chemical equilibrium principles? 
A) Haber process for ammonia 
B) Contact process for sulfuric acid 
C) Electrolysis of molten NaCl 
D) Ostwald process for nitric acid 
Answer: C 
Explanation: Electrolysis is a non-spontaneous process driven by electrical energy, not an equilibrium process. The others involve reversible reactions where equilibrium is manipulated for yield.

28: For the equilibrium: A(s) + 2B(g) ⇌ C(g) + D(g), which expression represents Kc? 
A) Kc = [C][D] / [B]² 
B) Kc = [C][D] / ([A][B]²) 
C) Kc = [B]² / [C][D] 
D) Kc = [A][B]² / [C][D] 
Answer: A 
Explanation: Pure solids (A) are omitted from equilibrium expressions. So Kc = [C][D] / [B]².

29: If the equilibrium constant for a reaction is very small (Kc


Remedial Exam dan repost
Chemistry Grade 11
Unit 5 Chemical Equilibrium

1: Which of the following is a characteristic of a reversible reaction? 
A) It proceeds to completion in one direction only 
B) The products cannot reform the reactants 
C) It can proceed in both forward and reverse directions simultaneously 
D) It always has a very large equilibrium constant 
Answer: C 
Explanation: Reversible reactions can proceed in both forward and reverse directions under the same conditions, eventually reaching a state of dynamic equilibrium.

2: At chemical equilibrium, which statement is TRUE? 
A) The concentrations of reactants and products are equal 
B) The forward and reverse reaction rates are equal 
C) All reactants have been converted to products 
D) The reaction has stopped completely 
Answer: B 
Explanation: At dynamic equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, so concentrations remain constant but reactions continue at the molecular level.

3: Which condition is NOT required for a system to attain chemical equilibrium? 
A) The system must be closed 
B) Temperature must remain constant 
C) The reaction must be irreversible 
D) The reaction must be reversible 
Answer: C 
Explanation: Chemical equilibrium can only be attained in reversible reactions; irreversible reactions proceed to completion and cannot reach equilibrium.

4: For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the correct equilibrium constant expression (Kc) is: 
A) Kc = [NH₃] / ([N₂][H₂]³) 
B) Kc = [NH₃]² / ([N₂][H₂]³) 
C) Kc = ([N₂][H₂]³) / [NH₃]² 
D) Kc = [N₂][H₂]³ / [NH₃] 
Answer: B 
Explanation: Kc = [products]ᶜᵒᵉᶠᶠⁱᶜⁱᵉⁿᵗˢ / [reactants]ᶜᵒᵉᶠᶠⁱᶜⁱᵉⁿᵗˢ, so Kc = [NH₃]² / ([N₂][H₂]³).

5: If Kc >> 1 for a reaction, this indicates that at equilibrium: 
A) Reactants are favored 
B) Products are favored 
C) Reactants and products are present in equal amounts 
D) The reaction does not proceed 
Answer: B 
Explanation: A large Kc value (much greater than 1) means the equilibrium mixture contains mostly products; the reaction favors the forward direction.

6: For the equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), Kc = 4.0 at a certain temperature. What is Kc for the reverse reaction: 2SO₃(g) ⇌ 2SO₂(g) + O₂(g)? 
A) 4.0 
B) 2.0 
C) 0.25 
D) 16.0 
Answer: C 
Explanation: The equilibrium constant for the reverse reaction is the reciprocal of the forward reaction: Kc(reverse) = 1/Kc(forward) = 1/4.0 = 0.25.

7: Which factor does NOT affect the value of the equilibrium constant Kc? 
A) Temperature 
B) Initial concentrations of reactants 
C) Presence of a catalyst 
D) Both B and C 
Answer: D 
Explanation: Kc depends only on temperature; it is unaffected by initial concentrations, pressure, volume, or catalysts (which only speed up attainment of equilibrium).

8: For the reaction: H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 50 at 448°C. If [H₂] = 0.1 M, [I₂] = 0.2 M, and [HI] = 0.5 M at a given moment, what is the reaction quotient Qc and which direction will the reaction proceed? 
A) Qc = 12.5; reaction proceeds forward 
B) Qc = 12.5; reaction proceeds reverse 
C) Qc = 25; reaction proceeds forward 
D) Qc = 25; reaction proceeds reverse 
Answer: A 
Explanation: Qc = [HI]²/([H₂][I₂]) = (0.5)²/(0.1×0.2) = 0.25/0.02 = 12.5. Since Qc < Kc (12.5 < 50), the reaction proceeds forward to reach equilibrium.

9: According to Le Chatelier's principle, if the pressure is increased on the equilibrium system: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the equilibrium will shift: 
A) To the left, favoring reactants 
B) To the right, favoring products 
C) No shift occurs 
D) Depends on temperature 

Answer: B 
Explanation: Increasing pressure favors the side with fewer moles of gas. Reactants: 4 moles gas; products: 2 moles gas. So equilibrium shifts right to reduce pressure.

10: For an endothermic reaction at equilibrium, increasing the temperature will: 
A) Shift equilibrium to the left, decreasing Kc 
B) Shift equilibrium to the right, increasing Kc 
C) Not affect the equilibrium position 
D) Shift equilibrium but Kc remains constant 
Answer: B 
Explanation: For endothermic reactions (ΔH > 0), heat is a reactant. Increasing temperature favors the forward reaction, shifting equilibrium right and increasing Kc.

11: Which change will NOT shift the equilibrium position for: CaCO₃(s) ⇌ CaO(s) + CO₂(g)? 
A) Adding more CaCO₃(s) 
B) Removing CO₂(g) 
C) Increasing the volume of the container 
D) Increasing the temperature (reaction is endothermic) 
Answer: A 
Explanation: Pure solids have constant concentration; adding/removing solids does not affect equilibrium position. Only changes in gas concentrations, pressure/volume, or temperature shift this equilibrium.

12: In the Haber process for ammonia synthesis: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = -92 kJ/mol, which condition favors maximum NH₃ yield? 
A) High temperature, low pressure 
B) Low temperature, high pressure 
C) High temperature, high pressure 
D) Low temperature, low pressure 
Answer: B 
Explanation: The reaction is exothermic (favors low T) and proceeds with fewer gas moles (favors high P). Industrially, a compromise (moderate T, high P, catalyst) is used for rate and yield.

13: The equilibrium constant Kp is used when equilibrium concentrations are expressed in terms of: 
A) Molarity (mol/L) 
B) Partial pressures 
C) Mass percentages 
D) Mole fractions only 
Answer: B 
Explanation: Kp is the equilibrium constant expressed using partial pressures of gaseous components; Kc uses molar concentrations.

14: For the reaction: 2NO(g) + O₂(g) ⇌ 2NO₂(g), if the volume of the container is suddenly doubled at constant temperature, the equilibrium will shift: 
A) To the left 
B) To the right 
C) No shift 
D) First left then right 
Answer: A 
Explanation: Doubling volume decreases pressure. The side with more moles of gas (reactants: 3 moles vs. products: 2 moles) is favored when pressure decreases, so shift left.

15: Which statement about catalysts and chemical equilibrium is CORRECT? 
A) Catalysts increase the value of Kc 
B) Catalysts shift equilibrium toward products 
C) Catalysts speed up attainment of equilibrium but do not change Kc or equilibrium position 
D) Catalysts only work for exothermic reactions 

Answer: C 
Explanation: Catalysts lower activation energy for both forward and reverse reactions equally, so equilibrium is reached faster but Kc and final concentrations remain unchanged.

16: For the equilibrium: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), Kc = 0.01 at a certain temperature. If 0.10 mol of PCl₅ is placed in a 1.0 L flask, what is the equilibrium concentration of Cl₂? (Use approximation x


Remedial Exam dan repost
21: What is the electron geometry of NH₃? 
A) Tetrahedral 
B) Trigonal planar 
C) Bent 
D) Linear 
Answer: A 
Explanation: NH₃ has four electron domains (three bonding pairs + one lone pair), giving a tetrahedral electron geometry; molecular geometry is trigonal pyramidal.

22: Which intermolecular force is strongest? 
A) London dispersion forces 
B) Dipole-dipole forces 
C) Hydrogen bonding 
D) All are equally strong 

Answer: C 
Explanation: Hydrogen bonding is a special strong type of dipole-dipole interaction occurring when H is bonded to N, O, or F, resulting in higher boiling points.

23: Which metal property is NOT explained by metallic bonding? 
A) Malleability 
B) Ductility 
C) Low thermal conductivity 
D) Luster 
Answer: C 
Explanation: Metals have high thermal conductivity due to mobile electrons transferring kinetic energy; low thermal conductivity is characteristic of nonmetals.

24: In valence bond theory, hybridization of one s and three p orbitals produces: 
A) sp hybrid orbitals 
B) sp² hybrid orbitals 
C) sp³ hybrid orbitals 
D) dsp³ hybrid orbitals 
Answer: C 
Explanation: Mixing one s and three p orbitals yields four equivalent sp³ hybrid orbitals arranged tetrahedrally, as in CH₄.

25: According to molecular orbital theory, a molecule is paramagnetic if it has: 
A) All electrons paired 
B) Unpaired electrons 
C) Only bonding electrons 
D) A bond order of zero 
Answer: B 
Explanation: Paramagnetism results from unpaired electrons that are attracted to magnetic fields; O₂ is paramagnetic due to two unpaired electrons in π* orbitals.

26: Which crystal type typically has the lowest melting point? 
A) Ionic 
B) Covalent network 
C) Metallic 
D) Molecular 
Answer: D 
Explanation: Molecular crystals are held by weak intermolecular forces (London, dipole-dipole, H-bonding), requiring less energy to melt than ionic, covalent network, or metallic crystals.

27: What is the correct Lewis structure for the carbonate ion (CO₃²⁻)? 
A) One C=O double bond and two C–O single bonds with resonance 
B) Three C=O double bonds 
C) Three C–O single bonds with carbon having a lone pair 
D) Two C=O double bonds and one C–O⁻ bond 
Answer: A 
Explanation: CO₃²⁻ has three resonance structures with one double bond and two single bonds (with formal charges); the actual structure is a resonance hybrid.

28: Which factor does NOT influence the strength of London dispersion forces? 
A) Molecular size/molar mass 
B) Molecular shape/surface area 
C) Polarity of the molecule 
D) Number of electrons 
Answer: C 
Explanation: London forces depend on polarizability, which increases with more electrons, larger size, and greater surface area; polarity affects dipole-dipole forces, not London forces.

29: In metallic bonding, why are metals malleable? 
A) Ions are held by rigid covalent bonds 
B) Layers of ions can slide past each other without breaking bonds due to delocalized electrons 
C) Electrons are fixed in position 
D) Metallic crystals have weak intermolecular forces 
Answer: B 
Explanation: The non-directional nature of metallic bonding allows metal ions to slide past one another while the electron sea maintains cohesion, enabling malleability.

30: Which statement correctly compares ionic and covalent compounds? 
A) Ionic compounds form between nonmetals; covalent between metal and nonmetal 
B) Ionic compounds have low melting points; covalent have high 
C) Ionic compounds conduct electricity when molten; covalent molecular compounds generally do not 
D) Covalent compounds are always gases at room temperature
 
Answer: C 
Explanation: Ionic compounds conduct when molten/dissolved due to mobile ions; most covalent molecular compounds lack charged particles and do not conduct electricity.

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🔗@ChemistryG9_12 ☑️


Remedial Exam dan repost
Chemistry Grade 11
Unit 2 Chemical Bonding


1: Which statement best describes the octet rule? 
A) Atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell 
B) All atoms must have exactly eight electrons in their outermost shell 
C) Only noble gases can have eight valence electrons 
D) Atoms with eight protons are most stable 
Answer: A 
Explanation: The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons, similar to noble gases.

2: Which type of chemical bonding involves the complete transfer of electrons from one atom to another? 
A) Covalent bonding 
B) Metallic bonding 
C) Ionic bonding 
D) Hydrogen bonding 
Answer: C 
Explanation: Ionic bonding occurs when electrons are transferred from a metal to a nonmetal, forming oppositely charged ions that attract each other.

3: What is the correct Lewis electron-dot symbol for nitrogen (Group 15)? 
A) :N: 
B) :N· 
C) ·N· with three dots around 
D) ·N· with five dots around 
Answer: D 
Explanation: Nitrogen has five valence electrons, so its Lewis symbol shows the element symbol N surrounded by five dots (one pair and three single electrons).

4: Which pair of elements is most likely to form an ionic compound? 
A) C and O 
B) Na and Cl 
C) N and H 
D) S and O 
Answer: B 
Explanation: Sodium (metal) and chlorine (nonmetal) have a large electronegativity difference, favoring electron transfer and ionic bond formation.

5: Which ion does NOT follow the octet rule in its stable ionic compound? 
A) Na⁺ 
B) O²⁻ 
C) Al³⁺ 
D) Li⁺ 
Answer: D 
Explanation: Li⁺ has only two electrons (helium configuration), which is stable for small atoms in Period 2; it is an exception to the octet rule.

6: Which property is characteristic of ionic compounds? 
A) Low melting points 
B) Conduct electricity in solid state 
C) Solubility in nonpolar solvents 
D) High melting and boiling points 
Answer: D 
Explanation: Ionic compounds have strong electrostatic forces between ions, requiring high energy to break, resulting in high melting and boiling points.

7: What is the molecular geometry of a molecule with four bonding pairs and no lone pairs on the central atom? 
A) Linear 
B) Trigonal planar 
C) Tetrahedral 
D) Bent 
Answer: C 
Explanation: According to VSEPR theory, four electron domains with no lone pairs adopt a tetrahedral geometry with bond angles of approximately 109.5°.

8: Which molecule has a bent molecular geometry? 
A) CO₂ 
B) CH₄ 
C) H₂O 
D) BF₃ 
Answer: C 
Explanation: Water has two bonding pairs and two lone pairs on oxygen, resulting in a bent geometry due to lone pair-bond pair repulsion.

9: Which intermolecular force is present in all covalent molecules? 
A) Hydrogen bonding 
B) Dipole-dipole forces 
C) London dispersion forces 
D) Ionic forces 
Answer: C 
Explanation: London dispersion forces (instantaneous dipole-induced dipole) exist in all molecules, whether polar or nonpolar, due to temporary electron distribution fluctuations.

10: Which compound exhibits hydrogen bonding? 
A) CH₄ 
B) HCl 
C) NH₃ 
D) CO₂ 

Answer: C 
Explanation: Hydrogen bonding occurs when H is bonded to N, O, or F. NH₃ has N–H bonds, allowing hydrogen bonding between molecules.

11: In the electron-sea model of metallic bonding, what are the "sea" electrons? 
A) Electrons tightly bound to individual atoms 
B) Delocalized valence electrons free to move throughout the metal lattice 
C) Core electrons involved in bonding 
D) Electrons transferred to nonmetals 

Answer: B 
Explanation: The electron-sea model describes metallic bonding as a lattice of positive metal ions surrounded by a "sea" of delocalized valence electrons that move freely.

12: Which property of metals is best explained by the electron-sea model? 
A) Brittleness 
B) Electrical conductivity 
C) Low density 
D) Transparency 
Answer: B 
Explanation: Delocalized electrons can move easily through the metal lattice when a voltage is applied, allowing metals to conduct electricity.

13: According to valence bond theory, a covalent bond forms when: 
A) Electrons are transferred between atoms 
B) Atomic orbitals overlap and electrons are shared between atoms 
C) Molecular orbitals are formed from linear combinations of atomic orbitals 
D) Ions attract each other electrostatically 
Answer: B 
Explanation: Valence bond theory states that a covalent bond results from the overlap of half-filled atomic orbitals, with electron pairs shared between the overlapping orbitals.

14: In molecular orbital theory, bonding molecular orbitals are: 
A) Higher in energy than the atomic orbitals from which they are formed 
B) Lower in energy than the atomic orbitals from which they are formed 
C) Always filled before antibonding orbitals 
D) Both B and C 
Answer: D 
Explanation: Bonding MOs are lower in energy than the parent atomic orbitals and are filled before antibonding orbitals according to the Aufbau principle.

15: What is the bond order of O₂ according to molecular orbital theory? 
A) 1 
B) 2 
C) 3 
D) 4 
Answer: B 
Explanation: O₂ has 12 valence electrons in MOs: (σ2s)²(σ*2s)²(σ2p)²(π2p)⁴(π*2p)². Bond order = ½[(8 bonding e⁻) – (4 antibonding e⁻)] = 2.

16: Which type of crystal is characterized by a lattice of positive ions surrounded by delocalized electrons? 
A) Ionic crystal 
B) Covalent network crystal 
C) Metallic crystal 
D) Molecular crystal 
Answer: C 
Explanation: Metallic crystals consist of metal cations arranged in a lattice with delocalized valence electrons moving throughout the structure.

17: Diamond is an example of which type of crystal? 
A) Ionic 
B) Covalent network 
C) Metallic 
D) Molecular 
Answer: B 
Explanation: Diamond has a giant covalent network where each carbon atom is covalently bonded to four others in a tetrahedral arrangement.

18: Which statement about Lewis structures is TRUE? 
A) They show the three-dimensional shape of molecules 
B) They represent only bonding electrons as dots 
C) They show valence electrons as dots around element symbols 
D) They cannot represent ions 
Answer: C 
Explanation: Lewis electron-dot structures depict valence electrons as dots placed around the chemical symbol of an element.

19: Which molecule violates the octet rule by having an expanded octet? 
A) BF₃ 
B) CO₂ 
C) PCl₅ 
D) NH₃ 
Answer: C 
Explanation: Phosphorus in PCl₅ has 10 valence electrons (five bonds), exceeding the octet; elements in Period 3 and beyond can expand their octet using d-orbitals.

20: Why do ionic compounds conduct electricity when molten or dissolved but not when solid? 
A) Ions are fixed in position in the solid state but free to move when molten/dissolved 
B) Electrons become delocalized only in solution 
C) The octet rule is satisfied only in solution 
D) Covalent bonds form in solution 

Answer: A 
Explanation: In solid ionic compounds, ions are locked in a rigid lattice; when molten or dissolved, ions become mobile and can carry electric current.

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Chemistry Grade 11
Unit 5 Chemical Equilibrium

1: Which of the following is a characteristic of a reversible reaction? 
A) It proceeds to completion in one direction only 
B) The products cannot reform the reactants 
C) It can proceed in both forward and reverse directions simultaneously 
D) It always has a very large equilibrium constant 
Answer: C 
Explanation: Reversible reactions can proceed in both forward and reverse directions under the same conditions, eventually reaching a state of dynamic equilibrium.

2: At chemical equilibrium, which statement is TRUE? 
A) The concentrations of reactants and products are equal 
B) The forward and reverse reaction rates are equal 
C) All reactants have been converted to products 
D) The reaction has stopped completely 
Answer: B 
Explanation: At dynamic equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, so concentrations remain constant but reactions continue at the molecular level.

3: Which condition is NOT required for a system to attain chemical equilibrium? 
A) The system must be closed 
B) Temperature must remain constant 
C) The reaction must be irreversible 
D) The reaction must be reversible 
Answer: C 
Explanation: Chemical equilibrium can only be attained in reversible reactions; irreversible reactions proceed to completion and cannot reach equilibrium.

4: For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the correct equilibrium constant expression (Kc) is: 
A) Kc = [NH₃] / ([N₂][H₂]³) 
B) Kc = [NH₃]² / ([N₂][H₂]³) 
C) Kc = ([N₂][H₂]³) / [NH₃]² 
D) Kc = [N₂][H₂]³ / [NH₃] 
Answer: B 
Explanation: Kc = [products]ᶜᵒᵉᶠᶠⁱᶜⁱᵉⁿᵗˢ / [reactants]ᶜᵒᵉᶠᶠⁱᶜⁱᵉⁿᵗˢ, so Kc = [NH₃]² / ([N₂][H₂]³).

5: If Kc >> 1 for a reaction, this indicates that at equilibrium: 
A) Reactants are favored 
B) Products are favored 
C) Reactants and products are present in equal amounts 
D) The reaction does not proceed 
Answer: B 
Explanation: A large Kc value (much greater than 1) means the equilibrium mixture contains mostly products; the reaction favors the forward direction.

6: For the equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), Kc = 4.0 at a certain temperature. What is Kc for the reverse reaction: 2SO₃(g) ⇌ 2SO₂(g) + O₂(g)? 
A) 4.0 
B) 2.0 
C) 0.25 
D) 16.0 
Answer: C 
Explanation: The equilibrium constant for the reverse reaction is the reciprocal of the forward reaction: Kc(reverse) = 1/Kc(forward) = 1/4.0 = 0.25.

7: Which factor does NOT affect the value of the equilibrium constant Kc? 
A) Temperature 
B) Initial concentrations of reactants 
C) Presence of a catalyst 
D) Both B and C 
Answer: D 
Explanation: Kc depends only on temperature; it is unaffected by initial concentrations, pressure, volume, or catalysts (which only speed up attainment of equilibrium).

8: For the reaction: H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 50 at 448°C. If [H₂] = 0.1 M, [I₂] = 0.2 M, and [HI] = 0.5 M at a given moment, what is the reaction quotient Qc and which direction will the reaction proceed? 
A) Qc = 12.5; reaction proceeds forward 
B) Qc = 12.5; reaction proceeds reverse 
C) Qc = 25; reaction proceeds forward 
D) Qc = 25; reaction proceeds reverse 
Answer: A 
Explanation: Qc = [HI]²/([H₂][I₂]) = (0.5)²/(0.1×0.2) = 0.25/0.02 = 12.5. Since Qc < Kc (12.5 < 50), the reaction proceeds forward to reach equilibrium.

9: According to Le Chatelier's principle, if the pressure is increased on the equilibrium system: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the equilibrium will shift: 
A) To the left, favoring reactants 
B) To the right, favoring products 
C) No shift occurs 
D) Depends on temperature 

Answer: B 
Explanation: Increasing pressure favors the side with fewer moles of gas. Reactants: 4 moles gas; products: 2 moles gas. So equilibrium shifts right to reduce pressure.

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