Summary of "Thermochemistry Equations & Formulas - Lecture Review & Practice Problems"

Summary of Main Ideas and Concepts

Internal Energy:
The change in Internal Energy (ΔE) of a system is given by the equation: ΔE = Q + W, where:
- Q = heat energy (positive if absorbed, negative if released)
- W = work done on the system (positive if work is done on the system, negative if done by the system)
Heat Transfer:
Heat flows from hot to cold, resulting in:
- Q is negative for exothermic processes (heat released).
- Q is positive for endothermic processes (heat absorbed).
Units of heat:
- 1 kJ = 1,000 J
- 1 calorie = 4.184 J
Work Calculation:
Work (W) is calculated using: W = P ΔV, where:
- P = pressure
- ΔV = change in volume
Work is negative when gas expands and positive when gas is compressed.
Heat Calculation:
Heat absorbed or released during a temperature change is calculated using: Q = m · C · ΔT, where:
- m = mass
- C = specific heat capacity
- ΔT = change in temperature
Phase Changes:
For Phase Changes, the heat can be calculated using: Q = m · ΔH, where ΔH is the enthalpy of fusion or vaporization.
Thermochemical Equations:
A thermochemical equation indicates whether a reaction is exothermic or endothermic based on the placement of heat energy in the equation.
Using Hess's Law:
Hess's Law allows the calculation of the enthalpy change of a reaction by using the enthalpy changes of related reactions.

To Calculate Change in Internal Energy:
1. Determine Q (heat absorbed or released).
2. Calculate W (work done on or by the system).
3. Use ΔE = Q + W to find the change in Internal Energy.
To Calculate Heat from Temperature Change:
1. Identify mass (m), specific heat capacity (C), and temperature change (ΔT).
2. Use Q = m · C · ΔT.
To Calculate Heat for Phase Changes:
1. Determine the mass of the substance and the corresponding ΔH (enthalpy of fusion or vaporization).
2. Use Q = m · ΔH.
To Use Hess's Law:
1. Modify the given reactions so that when added, they yield the target reaction.
2. Sum the enthalpy changes of the modified reactions to find the total enthalpy change for the target reaction.