17.1 The Flow of Energy—Heat and Work

• Heat always flows from a warmer object to a cooler object.
• A system gains heat in an endothermic process, and loses heat in an exothermic process.
• Heat flow is measured with two common units, the calorie and the joule.
• The heat capacity of an object depends on both its mass and its chemical composition.

17.2 Measuring and Expressing Enthalpy Changes

• In calorimetry, the heat released by a system equals the heat absorbed by its surroundings. Conversely, the heat absorbed by a system equals the heat released by its surroundings.
• The enthalpy change for a reaction can be treated like any other reactant or product.

17.3 Heat in Changes of State

• The heat absorbed by a melting solid is exactly the same as the heat lost when the liquid solidifies; that is, ΔH_fus= −ΔH_solid.
• The heat absorbed by a vaporizing liquid is exactly the same as the heat lost when the vapor condenses; that is, ΔH_vap= −ΔH_cond.
• Heat is either released or absorbed during the formation of a solution.

17.4 Calculating Heats of Reaction

• You can calculate the heat of a reaction by applying Hess’s law of heat summation or by using standard heats of formation.