MCAT Chemistry

Thermochemistry

MCAT Chemistry > Thermochemistry

Background

Thermochemistry is the branch of chemistry related to heat and the transfer of energy.

Systems

Systems involve the total reactants and products being observed in a reaction

Processes occur when a system changes on more of its properties such as the reactant & product concentration, temperature, or pressure

States are described by macroscopic properties and useful for comparing equilibrium points.

Pathway between states is described as mechanical work (W) or heat (Q).

States

State Functions

Standard State is the most stable state of a molecule under standard conditions

Standard States & Conditions is 1 atm at 25°C (298k)

Standard Temperature & Pressure (STP) is 1 atm at 0°C (273K)

Temperature (T) is the average kinetic energy of molecules

Total Internal Energy is based on the first law of thermodynamics, which states the total internal energy of a system is equal to the amount of thermal energy (heat) transferred to the system minus the work done by the system on the surroundings

ΔU = Q – W

Heat

See Heat

Enthalpy

See Enthalpy

Entropy

See Entropy

Gibbs Free Energy

See Gibbs Free Energy

Thermodynamic vs. Kinetic Control

Thermochemistry - Thermodynaic vs. Kinetic Control

Describes how some reactions that reach the intermediate stage will either decide to take a kinetic route or a thermodynamic route based on variable factors. Some products are thermodynamically favored and some are kinetically favored.

Kinetically favored products form quicker than thermodynamically favored ones because they take a quicker time to form due to lower activation energy. The activation energy is the primary distinction between these two states. However, some products are thermodynamically favored because they reside at a lower, more stable final energy state.

At higher temperatures, molecules tend to form the thermodynamically favored product, but at low temperatures tend to favor the kinetic one

MCAT Chemistry

Chemistry Topics