Question

You take two moles of the substance in part a) and one mole of the substance in part b) and place them together in an insulated container. Compare the magnitudes of the changes in thermal energy of the two substances as they come to thermal equilibrium. Assume there is no change in bond energy in the interval you are studying.

a) Substance in part a) has a greater change in thermal energy.

b) Substance in part b) has a greater change in thermal energy.

c) Both substances experience the same change in thermal energy.

d) The change in thermal energy cannot be determined without additional information.

Answer 1

When two substances reach thermal equilibrium, the change in thermal energy is the same for both substances, with one gaining what the other loses.

Step-by-step explanation:

When two substances are placed together in an insulated container and allowed to come to thermal equilibrium, the change in thermal energy for each substance depends on the direction and amount of heat transfer between them. Regardless of the number of moles of each substance, the principle of conservation of energy prevails, stating that energy cannot be created or destroyed. Thus, the change in thermal energy for the substance losing heat is equal in magnitude but opposite in sign to the substance gaining heat. Under the ideal situation in calorimetry, this implies c) Both substances experience the same change in thermal energy, with one losing heat and the other gaining the same amount, resulting in a net heat change of zero.