Thermal Properties of Matter

Name: ________________

Class: _________________

Index: ________________

Learning Objectives

• describe a rise in temperature of a body to an increase in internal energy (random thermal energy).• define the terms heat capacity and specific heat capacity.• recall and apply the relationship thermal energy = mass x specific heat capacity x change in temperature to new situations or to solve related problems.• describe melting/solidification and boiling/condensation in terms of energy transfer without a change in temperature.• explain the difference between boiling and evaporation.• define the terms latent heat and specific latent heat.• explain latent heat in terms of molecular behaviour.• recall and apply the relationship thermal energy = mass x specific latent heat to new situations or to solve related problems.• sketch and interpret a cooling curve.

Temperature

The atoms and molecules in a gas are in constant motion. Temperature is a measure of the speed with which they move. (More exactly it is a measure of their average kinetic energy.) The higher the temperature, the faster the molecules move.

Heat Capacity

The heat capacity C of an object is the heat energy needed to raise its temperature by 1 kelvin (or 1 degree celsius).

When different substances undergo the same temperaturechange they can store or release different amounts of heat.

Something with high heat capacity heats up slower andcools down faster.

Heat Capacity = Q / T

Q – thermal energy (J)

ΔT – temperature change (K)

Heat capacity does not take mass into account

– Different masses of the same substances absorb or release different amounts of heat

Specific Heat Capacity

• The specific heat capacity c of a substance is the heat energy needed to raise the temperature of 1 kg of the substance by 1 kelvin (or 1 degree celsius).

• Heat capacity per unit mass

c = Q / (m x T)

ΔT is always positive

• Heat always moves from hot to cold

Energy transfer without change in temperature – Melting / Freezing (Solidification)

- Condensation / Boiling (Evaporation)

Differences between Boiling and Evaporation

Factors affecting rate of evaporation

• Temperature – greater the temperature, faster the rate of evaporation.

• Wind - more wind blowing across the surface of the liquid means there will be constantly air with no water vapor in it right above the liquid, resulting in a faster evaporation.

• Surface Area - the greater the surface area exposed to the surroundings the faster it will evaporate.

• Humidity – greater the humidity (a lot of water vapor in the air), not allowing as much of the water to evaporate.

Latent Heat

• Heat absorbed or released as the result of a phase change is called latent heat (hidden heat).

• There is no temperature change during a phase change, thus there is no change in the kinetic energy of the particles in the material.

• The energy released comes from the potential energy stored in the bonds between the particles.

The latent heat of fusion Lf is the heat energy required to change an object from solid to liquid or liquid to solid without any temperature

change.

The latent heat of vaporization Lv is the heat energy required to change an object from liquid to gas or gas to liquid without any

temperature change.

Specific Latent Heat

The specific latent heat of fusion lf is the heat energy required to change a substance of mass 1 kg from solid to liquid or liquid to solid without any temperature change.

The specific latent heat of vaporization lv is the heat energy required to change a substance of mass 1 kg from

liquid to gas or gas to liquid without any temperature change.

Molecular behaviour in the change of states of substance

Cooling Curve

A cooling curve is a line graph that represents the change of phase of matter, typically from either a gas to a solid or a liquid to a solid.

Cooling Curve of Naphthalene

Liquid

Liquid + SolidSolid

A cooling curve is a line graph that represents the change of phase of matter, typically from a gas to a solid or a liquid to a solid. The independent variable (X-axis) is time and the dependent variable (Y-axis) is temperature. Below is an example of a cooling curve of castings.

The initial point of the graph is the starting temperature of the matter noted as the "pouring temperature". When the phase change occurs there is a "thermal arrest", that is the temperature stays constant. The amount of energy required for a phase change is known as latent heat. The "cooling rate" is the slope of the cooling curve at any point.

References:

http://science.howstuffworks.com/thermometer-info.htm/printable

http://uregina.ca/~sauchyn/geog221/latent_heat.bmp

http://image.tutorvista.com/content/matter-states/evaporation-and-boiling-difference.gif

http://www.mwit.ac.th/~physicslab/hbase/kinetic/imgkin/vapp2.gif

http://i130.photobucket.com/albums/p257/phobia_gurl/3states.jpg

http://upload.wikimedia.org/wikipedia/commons/1/18/Cooling_curve.png

http://en.wikipedia.org/wiki/Cooling_curve