Conversions & Constants

Introduction

In General Chemistry, it is essential to be familiar with common physical constants and unit conversions. These are frequently used in calculations involving thermodynamics, kinetics, and other core topics.

• Temperature Conversions:

  • °C = 5/9 (°F - 32)

  • K = °C + 273.15

• Energy and Power:

  • 1 W = 1 J/s

  • 1 J = 1 kg·m2/s2

• Gas and Thermodynamic Constants:

  • R = 0.08206 L·atm/K·mol = 8.314 J/K·mol

  • 101.3 J = 1 L·atm

Key Formulas

Thermodynamics and Energy

These formulas are fundamental for understanding heat, work, and energy changes in chemical systems.

• Heat Transfer:

• Change in Internal Energy:

• Work (at constant pressure):

• Enthalpy Change per Mole:

Enthalpy of Reaction

• Standard Enthalpy Change of Reaction:

• Where:

  • = stoichiometric coefficient

  • = standard enthalpy of formation

Electrostatics and Kinetic Energy

• Coulomb's Law (Electrostatic Energy):

• Kinetic Energy:

Chemical Kinetics

Chemical kinetics deals with the rates of chemical reactions and the factors affecting them.

• Rate Law for a Reaction A → B:

• General Rate Law (for A and B as reactants):

Integrated Rate Laws

• First-Order Reaction:

• First-Order (Logarithmic Form):

• Second-Order Reaction:

Arrhenius Equation

• Temperature Dependence of Rate Constant:

• Comparing Rate Constants at Two Temperatures:

Example Applications

• Example 1: To convert 25°C to Kelvin:

• Example 2: Calculating the enthalpy change for a reaction using standard enthalpies of formation.

• Example 3: Using the Arrhenius equation to determine the effect of temperature on reaction rate.