Thermochemistry The Basics of Heat

Transfer

The Flow of Energy

Thermochemistry - concerned with heat changes that occur during chemical reactions

Cranking up the Heat: Basic ThermodynamicsEnergy - capacity of an object

to do work or produce heat

Kinetic EnergyThe energy an object has due

to its motion

Potential EnergyStored energyEnergy of position

Energy in the universe is constant, though it changes forms.

Law of Conservation of energyLaw of Conservation of energy – energy can neither be created nor destroyed

Heat vs. TemperatureTemperature and heat are not the same thing.

Temperature describes the amount of motion of particles (the higher the temp., the faster the particles move because they have more energy).

Heat describes amount of energy transferred from one object to another

Describing Energy ChangesHeat flow is from the warmer object to

the cooler object

Heat Flow

Heat Flow

Describing Energy ChangesHot day 50°C = 122°F

Beans lost energy, it was transferred to its surroundings. This change of energy would be negative change = ∆

Energy transferred from fire to beans. Change in energy for beans would be positive.

Endothermic reactions – absorbs heat, ∆E is positive, the surroundings cool down

Exothermic reactions – releases heat, ∆E is negative, the surroundings heat up

Heat

Surroundings

Heat

Surroundings

Describing Energy Changes

Feels cold to the touch

Feels warm to the touch

Units used to describe Energy:

calorie – called “little calorie” – (cal)

kilocalorie – called “Big calorie”- (CAL) 1000 calories – same as a food calorie

Joule – the SI unit of heat - (J)

CONVERSION FACTOR

1 cal = 4.184 joules

1 cal 4.184 J

4.184 J 1 cal

Heat Units: Conversion Problems1. Convert 32.7 cal to joules.

2. Convert 6.24 J to cal.

3. Convert 10.2 Cal to cal.

4. Convert 10.2 Cal to joules.

5. Convert 8.16 joules to Cal.