Energy Changes
Chemistry · 50 practice questions
Energy changes (ΔH) accompanying physical and chemical changes (e.g. dissolution of/reaction with water for Na, NaOH, K, NH₄Cl); endothermic and exothermic reactions; entropy as an order-disorder phenomenon (e.g. mixing of gases, dissolution of salts); spontaneity of reactions (ΔG = 0 as the criterion for equilibrium; sign of ΔG for spontaneity).
- Determine the types of heat changes in physical and chemical processes and interpret graphical representations of them.
- Relate the physical state of a substance to its degree of orderliness.
- Determine the conditions for spontaneity of a reaction.
- Relate ΔH, ΔS and ΔG as driving forces for chemical reactions and solve simple problems using ΔG = ΔH − TΔS.
Try a few questions
- Practice question 1
A reaction with a positive ΔH (endothermic) is mainly more likely to become spontaneous at high temperature if it also has a
- A.positive ΔS (an increase in entropy)
- B.negative ΔS (a decrease in entropy)
- C.ΔS of exactly zero
- D.a ΔH that becomes even more positive at higher temperature
Show the answer
A. positive ΔS (an increase in entropy)
A large positive ΔS makes the -TΔS term increasingly negative at high T, eventually driving ΔG negative despite a positive ΔH.
- Practice question 2
The heat released when a strong acid neutralizes a strong base to form one mole of water is typically measured experimentally using a
- A.gas syringe, by measuring the volume of gas released
- B.chromatography setup, by measuring the distance travelled by each component
- C.pH meter alone, with no temperature measurement involved
- D.simple calorimeter, by recording the temperature rise of the reaction mixture
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D. simple calorimeter, by recording the temperature rise of the reaction mixture
A basic calorimeter captures the heat released as a measurable temperature increase during neutralization.
- Practice question 3
For an exothermic reaction, the activation energy of the forward reaction is generally
- A.lower than the activation energy of the reverse reaction
- B.higher than the activation energy of the reverse reaction
- C.exactly equal to the activation energy of the reverse reaction
- D.impossible to compare with the reverse reaction's activation energy
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A. lower than the activation energy of the reverse reaction
Since the products sit at a lower energy level than the reactants, the reverse reaction has to climb a bigger energy barrier.
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