The method and the results are on the entropy Gibbs energy lab. Do the analysis yourself first, then check the answers below.
Quick answer: Entropy measures how many ways particles and energy can be arranged; it rises from solid to liquid to gas. These answers go with the Chemistry 11-12 lab on entropy Gibbs energy: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers follow the sample measurements. Your own results will differ a little because heat is lost to the room, but your ΔH should be positive, your temperature fall should grow with the mass of solid and your explanation should mention entropy.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB R1.4
(25.7 − 23.3) ÷ 25.7 × 100 = 9.3 % lower than the data-book value.
Question 5 Entropy and spontaneity
ΔG = 23.3 − 294 × 0.1087 = 23.3 − 32.0 = −8.7 kJ/mol. The entropy increase as the ions spread through the solution gives a −TΔS term larger than the positive ΔH, so the process is spontaneous and the solution cools.
Question 6 Minimum entropy change
ΔG < 0 needs ΔS > ΔH ÷ T = 23 300 ÷ 294 = 79.3 J K⁻¹ mol⁻¹. The actual value of 108.7 is larger, so dissolving is spontaneous.
Question 7 Improving the lab
The cup gains heat from the room during the experiment, so the measured fall is smaller, giving a low ΔH. Improvement: use a lid, a temperature probe and plot temperature against time, extrapolating back to the time of mixing.
