Chapter 15 - Chemistry Notes

Thermochemistry: The branch of science that studies the transfer of energy during phase or chemical changes.
Thermal Energy: The total kinetic energy of the particles within a substance.
Temperature: The average kinetic energy in the particles of a sample, measured in °C or K.
Heat: The amount of thermal energy transferred from one substance to another, measured in joules (J).
Enthalpy (H): The thermal energy content of a system at constant pressure.

Measuring Thermal Energy

Thermal energy cannot be measured directly; it is measured through changes in temperature and heat.
Changes in enthalpy are measured using a calorimeter.
Calorimeter: An insulated container used to detect temperature changes during a chemical reaction.

Sensible Heat: The transfer of thermal energy that produces a temperature change in a substance.
Latent Heat: The transfer of thermal energy that produces a phase change without changing the temperature.
Molar Enthalpy of Fusion (ΔH_fus): The energy required to melt one mole of a solid to a liquid with no temperature change.
Molar Enthalpy of Vaporization (ΔH_vap): The energy required to vaporize one mole of a liquid to a gas with no temperature change.

Specific Heat (c_sp): The amount of energy required to raise the temperature of 1 g of a substance by 1 °C (J/g⋅°C).
High specific heat = slow temperature change, large energy requirement.
Low specific heat = rapid temperature change, small energy requirement.
Thermal energy input formula: $Q = m c_{sp} ΔT$

Define thermochemistry and explain its importance in phase changes.
What is the difference between thermal energy, temperature, and heat? Provide their units.
Describe the difference between sensible heat and latent heat with examples.
Explain the significance of specific heat in thermal energy calculations.
Calculate the energy needed to heat 25 g of water from 20 °C to 50 °C. Use c_sp = 4.18 J/g⋅°C.