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

Sample Problem 1 Find Q How much heat energy is needed to heat 10 grams of water by 10 degrees? The heat capacity of water is 4180

Sample Problem 2 Find 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

Sample Problem 3 Find 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

Sample Problem 4 Find 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. 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.

Latent Heat Capacity Problems Since there is only 3 variables, we will only have 3 types of problems to deal with.

Sample Problem 5 Find Q What is the energy absorbed if 10 grams of ice is melted? The is 333

Sample Problem 6 Find m If it takes 10000 J to evaporate a sample of water what is the mass of the sample? The is 2260

Sample Problem 7 Find 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