Heat Energy 2

•Heat Capacities•Sample Heat Capacity Problems•Latent Heat Capacity•Latent Heat Capacity Problems

Recall

• That radiation is how heat is transferred to the Earth from the Sun.

• Radiation is absorbed and reflected differently by various materials.

• The amount of heat energy that materials can hold differs as well. Specific Heat Capacity

• The overall amount of heat energy (Q) an object can hold depends on – Mass (m)– Temperature change (ΔT)– Specific heat capacity for the material (c)

Thermal (Heat) Energy vs Temperature

Heat Capacity Problems

• In order to solve a heat capacity problem we need to know 3 of the 4 variables

• The temperature change also has its own formula

• We will deal with 4 types of problems

TcmQ

if TTT

Sample Problem 1Find Q

• How much heat energy is needed to heat 10 grams of water by 10 degrees?– The heat capacity of water is 4180 °Ckg

J

Sample Problem 2Find m

• If an amount ice is heated from -20 to -10 degrees with 100 joules of heat energy, how much mass must be present?– The heat capacity of ice is 2120

°Ckg

J

Sample Problem 3Find ΔT

• If a 10 g sample of water vapor absorbs 10 J of heat, by how much will its temperature increase? – The heat capacity of water is 2.02 Cg

J

Sample Problem 4Find c

• Given that a 10 g substance has its temperature raise by 10 degrees by absorbing 50 J of heat energy, what is the substances heat capacity?

The Other Half of the Heat Capacity Story

• As a substance is heated through a phase transition, heat energy is absorbed from the surroundings as energy is used to break the intermolecular bonds.Examples:

Ice Water Water Steam• The reverse also applies that a substance

cooled through a phase transition will release heat as requires less energy in a more stable, bonded condition.Examples:

Water Ice Steam Water

Thermal (Heat) Energy vs Temperature

Latent Heat Capacity

• How can we calculate the heat energy absorbed/released by a substance undergoing a phase transition?– Mass should still be a factor but there is no

temperature change.

• Scientists simply experimentally measure the amount of heat per mass.

• Called latent heat capacity • There is two latent heat capacities for each

material; one for fusion (freezing) and one for vaporization.

H

Latent Heat Capacity Problems

• Since there is only 3 variables, we will only have 3 types of problems to deal with.

Sample Problem 5Find Q

• What is the energy absorbed if 10 grams of ice is melted?– The is 333 g

J

fusH

Sample Problem 6Find m

• If it takes 10000 J to evaporate a sample of water what is the mass of the sample?– The is 2260 g

J

vapH

Sample Problem 7Find ΔHfus

• Given that a 10 g substance has released 1000 joules of heat energy by freezing, what is the substance’s latent heat capacity of fusion?

Why is This Stuff Important?

• Sea Breezes

• Moderating effects of lakes and oceans

• Explains why winter lags the seasonal solar cycle.

• Overall thermal regulation of the Earth