CHM1101 Thermochemistry

Thermochemistry

• Energy is the capacity to do work and can be classified into different types: thermal energy (associated with the random motion of atoms and molecules), chemical energy (stored within the bonds of chemical substances), nuclear energy (stored within the collection of neutrons and protons in the atom), and potential energy (stored energy that depends on the relative position of various parts of a system).

Systems

• There are three types of systems: open systems (can exchange mass and energy), closed systems (allow the transfer of energy but not mass), and isolated systems (do not allow the transfer of either mass or energy).

Thermodynamics

• Thermodynamics is the scientific study of the interconversion of heat and other kinds of energy.
• Heat (q) is the transfer of thermal energy between two bodies at different temperatures.
• Temperature is a measure of the thermal energy, and it is different from thermal energy (temperature measures the average kinetic energy of the particles in a substance, while thermal energy measures the total kinetic energy).

First Law of Thermodynamics

• The First Law states that the energy of the universe is constant (E = q + w).
• Heat (q) is the energy transferred between two bodies, and work (w) is the force acting over a distance (w = F x d).

Thermodynamic State Functions

• Thermodynamic state functions are thermodynamic properties that depend only on the state of the system, not the pathway (examples: energy, pressure, volume, temperature).
• The change in thermodynamic state functions is calculated by subtracting the initial value from the final value (ΔE = Efinal - Einitial, ΔP = Pfinal - Pinitial, ΔV = Vfinal - Vinitial, ΔT = Tfinal - Tinitial).
• Other variables, such as q and w, depend on the pathway and are called path functions.

Thermochemistry

• Thermochemistry is the study of heat changes in chemical reactions.
• Exothermic processes are reactions that give off heat (transfer thermal energy from the system to the surroundings).
• Endothermic processes are reactions that require heat to be supplied from the surroundings to the system.