Thermochemistry

The study of energy and its transformations.

The transformations of energy, particularly heat, in chemical reactions.

• E_K = (1/2)mv²
• m = mass
• v = velocity

Joule = 0.23885cal = 6.2145 * 10¹⁸eV

Watt = J/sec

• E_P = mgh
• m = mass
• g = acceleration constant of gravity (6.67259 * 10^-11(m³/kg*sec²)
• h = height (relative to the surface in the earth)

The substance under study in which a change occurs.

Everything in the vicinity of the system.

The sum of the kinteic energy, potential energy, and the energy inherent to the particles.

E_tot = E_K + E_P + U

The energy that flows in or out of a system because of a temperature difference between the system and its surroundings.

The system absorbs energy (+q)

The system evolves energy (-q)

• The value of q required to return a system to the given temperature at the completion of a reaction.
• q_p = heat of reaction at a constant pressure (typically assume atomospheric)

An extensive property of a substance that can be used to obtain the change in q in a reaction. Enthalpy is a state function, i.e. it is a property of a system that depends only on its present state.

• Change in H = q_P
• Change in H = H_products - H_reactants

• Change in U = Change in H - P * (change in V)
• P = pressure
• V = volume

• Change in E = q + w
• q = heat
• w = work

The change in internal energy (U) of a system is the sum of the heat and work.

• The energy exchange that results when a force (F) moves and object through a distance (d).
• w = F * d

A measure of the heat transfered between a system and its surroundings.

The amount of heat required to raise the temperature of a sample by 1K.

• The amount of heat required to raise 1 gram of a substance 1K.
• Molar = the amount of heat required to raise the temperature of 1 mole of a substance 1K.

In a reaction carried out in a series of steps the change in enthalpy for the reaction will equal the sum of the enthalpy changes for the individual steps.