DP Chemistry (first assessment 2025)
Question 21N.1A.HL.TZ0.17
| Date | November 2021 | Marks available | [Maximum mark: 1] | Reference code | 21N.1A.HL.TZ0.17 |
| Level | HL | Paper | 1A | Time zone | TZ0 |
| Command term | State | Question number | 17 | Adapted from | N/A |
17.
[Maximum mark: 1]
21N.1A.HL.TZ0.17
In which of the following situations is the forward reaction spontaneous?
A. The equilibrium constant is greater than one under standard conditions.
B. The cell potential is negative.
C. The Gibbs free energy change of the reverse reaction is negative.
D. The entropy change of the universe for the forward reaction is negative.
[1]
Markscheme
A
Syllabus sections
Reactivity 1. What drives chemical reactions? » Reactivity 1.4—Entropy and spontaneity (Additional higher level) » Reactivity 1.4.1—Entropy, S, is a measure of the dispersal or distribution of matter and/or energy in a system. The more ways the energy can be distributed, the higher the entropy. Under the same conditions, the entropy of a gas is greater than that of a liquid, which in turn is greater than that of a solid. Predict whether a physical or chemical change will result in an increase or decrease in entropy of a system. Calculate standard entropy changes, ΔS⦵, from standard entropy values, S⦵.
Reactivity 1. What drives chemical reactions? » Reactivity 1.4—Entropy and spontaneity (Additional higher level) » Reactivity 1.4.3—At constant pressure, a change is spontaneous if the change in Gibbs energy, ΔG, is negative. Interpret the sign of ΔG calculated from thermodynamic data. Determine the temperature at which a reaction becomes spontaneous.
Reactivity 1. What drives chemical reactions? » Reactivity 1.4—Entropy and spontaneity (Additional higher level) » Reactivity 1.4.4—As a reaction approaches equilibrium, ΔG becomes less negative and finally reaches zero. Perform calculations using the equation ΔG = ΔG⦵ + RT lnQ and its application to a system at equilibrium ΔG⦵ = −RT lnK.