Question

Which statement is correct about heat?
(A) it is a measure of transfer of energy due to a temperature difference
(B) the heat transfer is always from hot to cold
(C) the heat absorbed by the surroundings equals the heat released by the system
(D) the amount of heat lost or gained during a reaction is directly related to the enthalpy change of the reaction
(E) all answers are correct

Answer 1

Hint: Change in Internal energy is equal to the heat absorbed by a system at constant volume. In flasks or test tubes, the chemical reactions take place at atmospheric pressure, but most of the chemical reactions are carried out at constant volume. Enthalpy is a state function, which is suitable to define under these conditions.

Complete step by step solution:
(A) it is a measure of the transfer of energy due to a temperature difference. When two systems have different temperatures, heat will exchange until two systems have the same temperature at equilibrium.
(B) The heat transfer is always hot to cold. When two bodies have different temperatures, one body at a higher temperature loses heat, and another body gains heat at a lower temperature.
(C) The heat absorbed by the surroundings equals the heat released by the system. For example, the system releases some amount of heat which is equal to the same heat that will heat absorbed by surroundings.
(D) the amount of heat lost or gained during a reaction is directly related to the enthalpy change of the reaction. The difference between the heat content of products and the heat content of reactants which gives enthalpy change.

So, option E is correct. All options about heat are correct.

Note: The enthalpy change for the exothermic reaction is negative, because of the heat released during the reaction, and enthalpy change for endothermic reactions are positive because heat absorbed from the surroundings.