Topic 4

Transformations and Conservation of

Energy

Energy- The ability to do work.

• Different forms include chemical, electrical, thermal, potential, and kinetic.

• Potential- stored energy available to do work.

• Kinetic- energy in motion.

Conservation of Energy• The law of conservation of

energy states that energy cannot be created or destroyed, but can change forms. These are transformations.

Energy Transformations

• Energy can be transformed into other forms.

• Example: In a solar panel the Sun (electromagnetic) is converted into into electrical energy.

Transformations

generator (electrical)

Battery(chemical)

defroster

(thermal)

ignition

(electrical)

Open and Closed Systems

• A closed system would not permit loss of matter outside the system. Energy is conserved. Example: insulation

• In an open system, energy is lost. Energy is not conserved.

Phase Changes• In a phase change energy is

absorbed into a system. For example, ice absorbs energy, increasing the motion of the molecules. Ice becomes a liquid. The energy required is called heat of fusion.

Phase Changes• When liquid water absorbs

energy, the molecules move faster, and the temperature of the water increases. The energy needed to raise 1 g 1°C is called the specific heat.

Phase Changes• When the energy of the

molecules becomes high enough the vapor pressure exceeds the atmospheric pressure, and the liquid boils. This energy is called heat of vaporization.

Energy Units• calorie- the amount of energy it

takes to raise 1 gram of water 1 degree Celsius.

• 1,000 calories = 1 Calorie• 1 calorie = 4.2 Joules• 1 kilojoule = 1,000 Joules

Heat of Fusion• It takes 334 Joules to change one

gram of ice to one gram of water.

• How many joules does it take to change 10 grams of ice to 10 grams of water?

Specific Heat• It takes 4.2 joules to raise one gram

of water 1 degree celsius.

• How many joules does it take to raise 10 grams of water 20 degrees celsius?

Heat of Vaporization• It takes 2,260 joules of energy to

change 1 gram of water from a liquid to a gas.

• How many joules would it take to change 30 grams of liquid water to a gas?

Total Energy

• You can add the heat of fusion, specific heat and heat of vaporization to get the total energy required to change a solid to a gas.

• You will find the heat required to change water from a solid to a gas in class.

The End