• What is the relationship between heat and temperature?

1. Temperature is related to the average kinetic energy of the particles in a substance.

2. SI unit for temp. is the Kelvin a. K = C + 273 (10C = 283K) b. C = K – 273 (10K = -263C)

Heat and Temperature

• The temperature of an object tells us how HOT it is

• Measured in degrees Celsius - °C• It is NOT the same as heat energy although

the two quantities are related.e.g. a beaker of water at 60 °C is hotter than a bath of water at 40 °C BUT the

bath contains more joules of heat energy

• Types of energy

• POTENTIAL ENERGY : STORED ENERGY. The energy inside

the substance.• KINETIC ENERGY : Associated with

motion. Average KE = TEMPERATURE

October 15

• What is heat and how do we measure it?

Heat a. The flow of thermal energy from one object to another. Heat always flows from warmer (HIGH T) to cooler(LOW T) objects.

Ice gets warmer while hand gets cooler

Cup gets cooler while hand gets warmer

Energy• The ability to do work.• Energy is measured in Joules (J)• Any change re quires energy. Changes can

be Exothermic or Endothermic• Exothermic changes- release or give off

heat while they occur. (condensation, freezing)

• Endothermic changes Absorb heat as they occur (melting, boiling)

ENERGY AND CHEMICAL REACTIONS

• EXOTHERMIC REACTIONS: reactions that RELEASE heat as they occur. Example: any combustion.

• ENDOTHERMIC REACTIONS: reactions that ABSORB heat energy as they occur.

Heating and Cooling

• If an object has become hotter, it means that it has gained heat energy.

• If an object cools down, it means it has lost energy

6. Specific Heat a. Some things heat up or cool

down faster than others.

Land heats up and cools down faster than water

HEAT CAPACITY

• The amount of heat needed to increase the temperature of a material by 1oC. It depends on the MASS and the CHEMICAL COMPOSITION of the material.

  

SPECIFIC HEAT CAPACITY

• The amount of heat needed to increase the temperature of 1 g of substance by 1 C.

• Depends only on the chemical composition. 

SPECIFIC HEAT CAPACITYMATERIAL SPECIFIC HEAT J/g C

Water 4.18

Alcohol 2.43

Aluminum 0.90

Iron 0.45

Lead 0.13

Sand 0.83

Why does water have such a high specific heat?

Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds

and do not need as much energy to break them.

water metal

How to calculate changes in HEATThe heat absorbed or released in

a chemical reaction

Q = m x T x CpQ = HEATm = mass of substanceT = change in temperature (Tf – Ti)Cp = specific heat of substance

Calorimeter

Bomb Calorimetry

A more sophisticated model is the bomb calorimeter, it has a chamber where a chemical reaction takes place and a device to start the reaction.

HEAT OF FUSION FOR WATER (TABLE B)

• Amount of heat needed to completely melt 1g of water.

• 334 J/g• 334 Joules of heat are necessary to

completely melt 1 g of water.• HOW MUCH HEAT IS NEEDED TO

MELT 10 g OF WATER?

HEAT OF VAPORIZATION FOR WATER (TABLE T)

• The amount of heat needed to completely vaporize one g of water at its boiling point.

• 2260 J/g

• Water needs 2260 J of heat per gram to convert to gas!