Energy & Heat

Tuesday Sept. 9th, 2008

Energy Energy is the ability to do work Energy exists in many different forms

Can you think of any?• Kinetic Energy• Potential Energy• Chemical Energy• Thermal Energy• Nuclear Energy• Sound Energy• Light Energy

Law of Conservation of Energy- energy cannot be created or destroyed, it simply changes forms

Chemical Energy Energy within matter due to its chemical

makeup. Chemical reactions convert chemical energy to

other forms of energy (light, heat, etc.)

Examples? Batteries Food

Kinetic Energy Energy of motion

How is this different from potential energy?

Particles (atoms) are always in motion. They have kinetic energy

Heat Heat is the sum of the kinetic energy of the particles in

a sample Temperature is the measurement of heat. Temperature is a measure of the average kinetic

energy of the particles in a sample

http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

Watch what happens to the particles as the temperature is increased

Endothermic & Exothermic An exothermic reaction feels hotter

because heat is exiting the reaction. Heat is moving from the system (the

reaction) to the surroundings (your hand)

An endothermic reaction feels colder because heat is entering the reaction. Heat is moving from the surroundings

(your hand) to the system (the reaction)

THERE IS NO SUCH THING AS COLD IN SCIENCE CLASS!!! ONLY HEAT CAN MOVE!

How would you convert from Celsius to Kelvin??

Specific Heat Capacity The amount of heat energy required to raise

the temperature of 1 g of a substance by 1 ºC.

The specific heat of water is 1.00 cal / g ºC 1000 cal = 1 Calorie (from your nutrition labels)

The specific heat of water is 4.184 J/ g ºC Both Jules (J) and calories (cal) are units of energy

Comparing Heat Capacities Given: The heat capacity of water is 4.184 J/g ºC The heat capacity of copper is 0.385 J/g ºC

Which one requires more Jules to raise the temperature of 1 gram 1 ºC ?

Does this mean that water feels hotter faster or slower than copper?

Energy and Temperature During a Phase Change

As energy is increasing what is happening to temperature? (blue)

Why might energy increase but temperature stay constant? (green)

Temp Energy