9 What is the difference between heat (q) and enthalpy (H)? Enthalpy is the heat associated with gas-phase reactions. Heat (q) and enthalpy (H) are not different. Heat (q) is the enthalpy (H) of a reaction at constant pressure. O Enthalpy (H) is the heat (a) of a reaction at constant pressure. 10 A reaction releases 50 kJ of heat to the surroundings. It is not known if the reaction is constant pressure or constant volume. What is the sign of AH? 199 O It is negative because the reaction is exothermic. O If the reaction is constant pressure, it is negative. If the reaction is constant volume, it does not make sense to discuss enthalpy. O If the reaction is constant pressure, it is negative. If the reaction is constant volume, it is positive. If the reaction is constant pressure, it is positive. If the reaction is constant volume, it is negative 19