Endothermic Reactions (need heat)(Absorb heat energy from their surroundings)

Solid + heat Liquid (Fusion/Melting)Liquid + heat Gas (Boiling/Evaporation/Vaporization)Solid + heat Gas (Sublimation)

These changes need HEATINGThey need to take in or gain heat

(Endothermic)

Exothermic Reactions (give off heat)(Release heat energy to their surroundings)

Gas Liquid + heat (Condensation)Liquid Solid + heat (Freezing/Solidification)Gas Solid + heat (Deposition)

These changes require COOLINGIn order to COOL OFF, the heat they contain must be given off

(Exothermic)

Temperature vs Heat

What’s the difference?

It takes more heat to boil a bucket of water than it takes to boil a cup of water even though they both end up at the same temperature.

Why?

Temperature vs Heat

Temperature1. Tells how hot or cold2. Use Thermometer (o C, o F, or K)3. Measures the average KE

of the particles 3. Kinetic energy = speed of

particles4. As Avg KE increases,

temperature increases

Heat1. Heat is a form of energy2. Use Calorimeter (Joules or Calories)3. Measures the total KE of all

the particles4. Heat is a transfer of energy

(usually thermal energy) from a hotter area to a colder area

5. Thermal energy = energy associated with random motion of particles

Temperature vs Heat*** Heat energy always flows from an area of higher

temperature to an area of lower temperature! ****

Substance Direction of heat flow Substance at 40oC from hot to cold at 80oC

***In summary: Temperature depends on the speed of the particles (avg KE) while heat depends on the speed & quantity of particles (total KE).

Temperature Scaleshttp://www.youtube.com/watch?v=RO-qC-Wj7Nk&feature=related

Carefully draw the diagram. Then, write down the following info:

1. Absolute Zero = Zero Kelvin (molecules stop moving, coldest temp)

2. NBP of water is called an water-steam equilibrium = 100oC

3. NFP of water is called an water-ice equilibrium = 0oC

4. Notice: There are 100 degrees between boiling & freezing on both the Kelvin and Celsius scales.

Temperature Conversions

• One degree on the K scale is the same size as one degree on the C scale.

• Equation K = oC + 273

Given: oC = 26 oC Unknown: K = ?

K = 26 + 273 = 299 K

Temperature Conversions

• Equation K = oC + 273

Given: K = 200 K Unknown: oC = ? 200 = oC + 273oC = 200 - 273

= -73 oC

Temperature Conversions

If the temp changed from 283 K to 293 K, how many oC did it change ?

293 K – 283 K = 10 KAnswer: 10 oC

Why?

Temperature

Question: Which substance has particles with the

highest average KE?

a) 50 grams of Fe(s) at 35oC b) 75 grams of Hg (l) at 25oC c) 100 grams of He (g) 20oC

Answer: A (highest temp)

Law of Conservation of Energy

1. Energy cannot be created or destroyed, but may change form

2. The total amount of energy in the universe is constant

3. Energy lost = Energy gained

Law of Conservation of Energy

Problem: A student puts an ice pack on his swollen ankle.

1) Which way does the heat flow?

Answer: From his ankle to the ice pack

2) How does this illustrate the Law?

Answer: The heat lost by the ankle = the heat gained by the ice pack.

Law of Conservation of Energy

Device: Kitchen Toaster1) What is the energy transformation?

Answer: From electrical energy to heat energy

2) How does this illustrate the Law?

Answer: Energy is not created or destroyed, but it does change form from electrical to heat energy.