CHEM 111: Thermochemistry Summary

Chapter 6: Thermochemistry Summary

Energy Concepts

• Energy: Capacity to do work or transfer heat.
• Work (w): $w = F \times d$
• Heat: Energy that causes temperature increase; flows from warm to cool objects.

Forms of Energy

• Kinetic Energy (KE): Energy of moving objects.
• Formula: $KE = (1/2)mv^2$.
• Potential Energy (PE): Stored energy due to position/composition.
• Formula: $PE = mgh$ (where $g = 9.8 m/s^2$).

Energy Changes in Chemistry

• Exothermic Process: Releases energy (negative enthalpy, $- \Delta H$).
• Endothermic Process: Absorbs energy (positive enthalpy, $+ \Delta H$).

Laws of Thermodynamics

• First Law: Energy can neither be created nor destroyed; total energy change: $E_{total} = KE + PE$.
• Heat Transfer: Heat flows from hot to cold; involves internal energy changes.

Calorimetry

• Heat Capacity (C): Energy to raise temperature by $1 K$.
• Specific Heat Capacity ($C_s$): Energy needed to raise $1 g$ by $1 K$.
• Formula: $(C_s = \frac{q}{m \times \Delta T})$
• Molar Heat Capacity ($C_{molar}$): Energy to raise the temperature of $1 mol$ by $1 K$.

Thermochemical Equations

• $\Delta H$ = Heat change during reaction at constant pressure.
• Enthalpy Change ($\Delta H$):
  • Exothermic: Energy released ($\Delta H$ is negative).
  • Endothermic: Energy absorbed ($\Delta H$ is positive).

Key Calculation Formulas

• Energy (q): $q = C_s \times m \times \Delta T$
• Calorimeter Heat Transfer: $q_{rxn} = -q_{soln}$.

Practical Examples

• Specific heat calculations in reactions measured by calorimeters, including calculations for different types of reactions (exothermic vs. endothermic).
• Importance of proper measurements and assumptions in calorimetric calculations.

Summary of Key Equations and Symbols

This section summarizes the main formulas presented in the notes along with definitions for each symbol:

1. Work (w):

   • Equation: $w = F \times d$
   • w: Work done (energy transfer resulting from a force acting over a distance).
   • F: Force (in Newtons, N).
   • d: Distance (in meters, m).

2. Kinetic Energy (KE):

   • Equation: $KE = (1/2)mv^2$
   • KE: Kinetic Energy (energy of motion, in Joules, J).
   • m: Mass of the object (in kilograms, kg).
   • v: Velocity of the object (in meters per second, m/s).

3. Potential Energy (PE):

   • Equation: $PE = mgh$
   • PE: Potential Energy (stored energy due to position, in Joules, J).
   • m: Mass of the object (in kilograms, kg).
   • g: Acceleration due to gravity ($9.8 m/s^2$).
   • h: Height (or vertical distance, in meters, m).

4. Heat Transfer (q):

   • Equation: $q = C_s \times m \times \Delta T$
   • q: Amount of heat energy transferred (in Joules, J).
   • C_s: Specific Heat Capacity (energy needed to raise $1 g$ of a substance by $1 K$ or $1 \degree C$, in $J/(g \cdot K)$ or $J/(g \cdot \degree C)$).
   • m: Mass of the substance (in grams, g).
   • $\Delta T$: Change in temperature ($T_{final} - T_{initial}$) (in Kelvin, K, or degrees Celsius, $^\circ C$).

5. Calorimeter Heat Transfer:

   • Equation: $q_{rxn} = -q_{soln}$
   • q_rxn: Heat change of the chemical reaction (in Joules, J).
   • q_soln: Heat change of the solution (or the calorimeter, in Joules, J). The negative sign indicates that heat released by the reaction is absorbed by the solution, and vice-versa.