Two different reactions are carried out separately in identical coffee-cup…
CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
Two different reactions are carried out separately in identical coffee-cup calorimeters containing equal masses of water at the same initial temperature.
• Reaction X causes the water temperature to rise by 3∘C.
• Reaction Y causes the water temperature to drop by 2∘C.
Which statement best accounts for the observed temperature changes?
(a) Both reactions are exothermic because temperature changes always indicate heat is released to the surroundings.
(b) Reaction X is endothermic because the system absorbs heat, so the water must warm to compensate, whereas Reaction Y is exothermic because the system releases heat, cooling the water.
(c) Reaction X is exothermic because the system releases heat, increasing the kinetic energy of the water molecules, whereas Reaction Y is endothermic because the system absorbs heat, decreasing the water’s kinetic energy.
(d) Both reactions are endothermic because energy is required to break bonds in the reactants, leading to temperature changes in the water.