Week 7: Chemical thermodynamics - Part 1

What is thermodynamics?

Describes energy movement

What is heat energy?

Heat is the energy that transfers from a hotter to a cooler objects in this process

What is an open system?

Can gain or lose mass and energy across their boundaries.

What is a closed system?

Can absorb or release energy, but not mass, across the boundary. The mass of a closed system is constant, no matter what happens inside.

What is a isolated system?

Cannot exchange matter or energy with their surroundings. Because energy cannot be created or destroyed, the energy of an isolated system is constant, no matter what happens inside.

What is internal energy (U)?

The sum of all energies in a sample of matter

In an isolated system change in internal energy is 0.

What is enthalpy (H)?

Amount of heat absorbed or evolved by a chemical system

Often observed with temperature change during a reaction under conditions of constant pressure 

What is entropy?

A measure of the number of ways energy is distributed throughout a chemical system.

What is Gibbs energy (G)?

the maximum amount of usable energy in a system

G = H - TS 

Endothermic reactions

Absorbs energy

Exothermic reactions

Releases energy

What is a state function?

State functions have unique values once the state of the system is defined.

What is path functions?

Functions like heat and work have no meaning when the system is not undergoing change.

Path functions are like details on a route while the point of departure and destination are like state functions.

Equation for enthalpy

H = U + pV

where

H is the enthalpy of the system (J)

U is the internal energy of the system, (J)

p is the pressure of the system, (Pa)

V is the volume of the system. (m³)

Enthalpy alone cannot be measured so we measure change in enthalpy

What is the enthalpy of formation?

the enthalpy of formation is the change that accompanies the formation of 1 mole of a substance in its standard state.

Phase changes

q=mcΔT

(during heating of a phase)

q=mΔH

(at constant pressure, during phase transitions)