physics : thermal properties of materials

definition of specific heat capacity

quantity of thermal energy Q per unit mass m required to raise the temperature of a substance by one degree

formula for specific heat capacity c

c = Q/mΔθ

J kg¯ ¹ K¯ ¹

definition of specific latent heat

the quantity of thermal energy required per unit mass to change the state of a substance without any change in temperature

specific latent heat of fusion Lf

solid to liquid

Lf = Q/m

J kg¯ ¹

specific latent heat of vaporisation Lv

liquid to vapour

Lv = Q/m

J kg¯ ¹

internal energy definition

the sum of random distribution of kinetic energy and potential energy associated with the molecules of a system

unit for internal energy

J - joules

in U, what is potential energy due to

Ep is due to the intermolecular forces, which depend on the separation of molecules.

as separation increases (ie more disordered), Ep increases

what does U of an ideal gas depends on

kinetic energy only (and therefore is only affected by temperature)

this is because for ideal gases, the Ep of the molecules is zero since there is no intermolecular forces

U of the system depends only on its state (like temperature, pressure). If it goes to the same state, ΔU=0

what is the first law of thermodynamics

the increase in the internal energy ΔU of the system is the sum of the heat supplied Q to the system and work done W on the system

first law of thermodynamics formula

ΔU = Q + W

if heat is supplied to the system

Q is positive

if heat is taken from the system

Q is negative

compression ie work done ON gas

W is positive

expansion ie work done BY gas

W is negative

how to calculate work done of a system

area under pressure-volume graph

W = pΔV