LAW OF THERMODYNAMICS

 Laws of Thermodynamics

Thermodynamics

1. Thermodynamics is the study of the effects of work, heat, and energy on a system

2. Thermodynamics is only concerned with macroscopic (large-scale) changes and observations

3. All of the thermodynamics can be expressed in terms of four quantities

# Temperature (T)

# Internal Energy (U)

# Entropy (S)

# Heat (Q)

 1^st law

1. The first law of thermodynamics is an extension of the law of conservation of energy

2. The change in internal energy of a system is equal to the heat added to the system minus the work done by the system

                                                            ΔU = Q - W

FIRST LAW OF THERMODYNAMICS

ANY THERMODYNAMIC SYSTEM IN AN EQUILIBRIUM STATE POSSESSES A STATE VARIABLE CALLED THE INTERNAL ENERGY. BETWEEN ANY TWO EQUILIBRIUM STATES, THE CHANGE IN INTERNAL ENERGY IS EQUAL TO THE DIFFERENCE OF THE HEAT TRANSFER INTO THE SYSTEM AND WORK DONE BY THE SYSTEM.

Process Terminology

1. Adiabatic – no heat transferred

2. Isothermal – constant temperature

3. Isobaric – constant pressure

4. Isochoric – constant volume

Adiabatic Process

1    # An adiabatic process transfers no heat

                          therefore Q = 0

2.                                                       ΔU = Q – W

3.      When a system expands adiabatically, W is positive (the system does work) so ΔU is negative.

4.      When a system compresses adiabatically, W is negative (work is done on the system) so ΔU is positive.

Isothermal Process

1.      An isothermal process is a constant temperature process. Any heat flow into or out of the system must be slow enough to maintain thermal equilibrium

2. For ideal gases, if ΔT is zero, ΔU = 0

3.Therefore, Q = W

4. Any energy entering the system (Q) must leave as work (W)

Isobaric Process

 An isobaric process is a constant pressure process. ΔU, W, and Q are generally non-zero, but calculating the work done by an ideal gas is straightforward

                                  W = P·ΔV

Water boiling in a saucepan is an example of an isobar process

Isochoric Process

An isochoric process is a constant volume process. When the volume of a system doesn’t change, it will do no work on its surroundings. W = 0

                                    ΔU = Q