Heat Changes in Temperature and Phase

Specific Heat Capacity Specific heat capacity – the quantity of energy needed to raise the temperature of 1 kg of a substance by 1°C at constant pressure How much energy is needed to change the temperature of something Different for every substance Specific heat capacity = energy transferred as heat / (mass * change in temperature) c p = Q/(mΔT) The subscript p means that the pressure is constant We will assume this during our calculations Q = mcΔT

Specific Heat Capacity When the temperature increases, ΔT and Q are positive When the temperature decreases, ΔT and Q are negative T can be in either °C or K 1°C is the same as 1K Q is in Joules c is in J/(kg*°C ) or J/(kg* K)

Specific Heat Capacity

To determine a specific heat capacity, you must compare the unknown substance to a known substance such as water The energy absorbed or lost by the water must be equal to the energy absorbed or lost by the unknown Calorimetry – an experimental procedure used to measure the energy transferred from one substance to another as heat − The container of the unknown is called a calorimeter Q w = -Q x c p,w m w ΔT w = -c p,x m x ΔT x

Latent Heat Phase change – the physical change of a substance from one state (solid, liquid, or gas) to another at constant temperature and pressure Energy is required for a change of state Must be added to go to a higher energy state (gases, plasmas) Released when moving to a lower energy state (solids)

Latent Heat This energy changes the internal energy of the substance not the temperature Temperature will not change until all of the substance has completely undergone the phase change

Latent Heat Heat is the energy that is exchanged between two objects at different temperatures or between two objects at the same temperature when one of them is undergoing a phase change Atoms and molecules prefer to maintain a distance from similar atoms or molecules that correspond to a minimum potential energy

Latent Heat As heat is added to a substance its particles increase in energy Once enough energy has been added, bonds holding the atoms or molecules break Resulting in phase changes or chemical reactions if enough energy is added

Latent Heat

Energy required to melt a substance goes into rearranging the molecules of that substance Heat of fusion – the energy per unit mass transferred in order to change a substance from solid to liquid or from liquid to solid at constant temperature and pressure

Latent Heat

Energy required to vaporize a substance mostly goes into separating the molecules Heat of vaporization – the energy per unit mass transferred in order to change a substance from liquid to vapor or from vapor to liquid at constant temperature and pressure Latent heat – the energy per unit mass that is transferred during a phase change of a substance

Latent Heat

Energy transferred as heat during a phase change = mass * latent heat Q = mL L f – latent heat of fusion L v – latent heat of vaporization

Latent Heat