Question at position 14 Consider the reaction where A = white spheres and B = black spheres. A ⇌ B ΔH°= –45 kJ/mol Identify the figure showing the new equilibrium after the temperature is increased. Figure B Figure C Figure D Figure A单项选择题
A
Figure B
B
Figure C
C
Figure D
D
Figure A

Question

Question at position 14 Consider the reaction where A = white spheres and B = black spheres. A ⇌ B ΔH°= –45 kJ/mol Identify the figure showing the new equilibrium after the temperature is increased. Figure B Figure C Figure D Figure A单项选择题

A

Figure B

B

Figure C

C

Figure D

D

Figure A

BlackTom AI · Accepted Answer

Because ΔH° = −45 kJ/mol, the forward reaction A → B is exothermic (heat is released as a product). Treating heat as a product lets Le Chatelier’s principle be applied directly: adding heat (increasing temperature) drives the equilibrium in the direction that absorbs heat (the endothermic direction), which here is the reverse reaction B → A.

Step-by-step reasoning:
1. Identify thermochemistry: ΔH° < 0 ⇒ forward (A → B) is exothermic; reverse (B → A) is endothermic.
2. Apply Le Chatelier’s principle: increasing temperature adds heat to the system, so the system will shift to consume that added heat — i.e., toward the endothermic direction (reverse), producing more A.
3. Use the van ’t Hoff relation for a qualitative check: d(ln K)/dT = ΔH°/(R T^2). With ΔH° negative, d(ln K)/dT < 0, so K (=[B]/[A]) decreases as T increases. A smaller K means [B] relative to [A] drops — more A, fewer B at the new equilibrium.
4. Compare the pictured options: the correct new equilibrium must show an increased proportion of A (white spheres) and a decreased proportion of B (black spheres) compared with the original diagram.

Why other options are incorrect:
- Figure B and Figure C show equal or greater amounts of B (black) than before, which would correspond to a shift toward products (right) — the opposite of what raising T causes for an exothermic forward reaction.
- Figure D shows only a slight change or still mostly B, not the larger increase in A expected for the shift to the reactant side.

Therefore the new equilibrium after increasing temperature is represented by Figure A, which shows a clear increase in white spheres (A). This matches the provided correct answer: Figure A.

Question at position 14 Consider the reaction where A = white spheres and B = black spheres. A ⇌ B ΔH°= –45 kJ/mol Identify the figure showing the new equilibrium after the temperature is increased. Figure B Figure C Figure D Figure A单项选择题

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