Thermochemistry

Definition

Thermochemistry is the study of the heat energy involved in chemical reactions and changes of state. It focuses on how energy is absorbed or released during these processes.

5 Must Know Facts For Your Next Test

1. The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted.
2. Enthalpy ($\Delta H$) is a measure of the total energy of a system, including internal energy and the energy required to make space for it by displacing its environment.
3. Exothermic reactions release heat into their surroundings, resulting in a negative $\Delta H$ value.
4. Endothermic reactions absorb heat from their surroundings, resulting in a positive $\Delta H$ value.
5. Hess's Law states that the total enthalpy change for a reaction is the same, no matter how many steps the reaction is carried out in.

Review Questions

• What does the first law of thermodynamics state about energy?
• How can you differentiate between exothermic and endothermic reactions based on $\Delta H$ values?
• Explain Hess's Law and its significance in thermochemistry.

Related terms

Enthalpy: A thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.

Calorimetry: The measurement of heat transfer in physical changes and chemical reactions using a device called a calorimeter.

Specific Heat Capacity: The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.