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THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Jan 03, 2016

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Page 1: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

THERMO-CHEMISTRY

Page 2: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Thermochemistry

Study of the heat changes that occur during a chemical

reaction

Page 3: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

EnergyThe capacity to do work or generate

heat

Page 4: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

In chemistry, energy is stored

in chemical bonds

Page 5: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

When bonds are made, energy is released. When

bonds are broken, energy is absorbed.

Page 6: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

The main form of energy in

chemistry is HEAT!

Page 7: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat (q)Energy that is

transferred between objects that have a

temperature difference

Page 8: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat always moves from a

higher temp to a lower temp

Page 9: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Terms to know: universesystem

surroundings

Page 10: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Law of Conservation of Energy

In any process, energy is neither

created nor destroyed

Page 11: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Some reactions absorb energy

(heat) and some give off energy

(heat).

Page 12: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Exothermic Reaction

A reaction that releases heat into the surroundings

(heat exits)

Page 13: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Endothermic Reaction

A reaction that absorbs heat from the surroundings

(heat goes en)

Page 14: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Enthalpy Change (H)

Amount of heat lost or gained in a

reaction(unit = kJ)

Page 15: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Sign of H

Process Heat

Positive Endo-thermic

Absorbed

Negative Exo-thermic

Released

Page 16: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.
Page 17: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Temperature (T)

A measure of the average kinetic energy

of the particles in a substance

Page 18: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat (Q)Energy that is

transferred between objects that have a

temperature difference

Page 19: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat (Q)Is measured in Joules (J)

(or kJ)

1 kJ = 1000 J

Page 20: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

So…how do we measure heat?

We can only measure changes in heat

(absolute heat doesn’t exist)

Page 21: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Specific HeatAmount of heat needed to

raise the temp of 1g of a substance 1C

gC

J

Unit =

Page 22: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

The Heat EquationQ = mCpT

Q = heat (joules-J)m = mass (grams)

Cp = specific heat (J/g C)T = change in temp (C)

Page 23: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

How much heat is needed to raise the temperature of 350

grams of water from 0.0°C to 25°C?

37000 Joules

Page 24: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

A 450 gram sample of water cools from

55°C to 10.0°C. How much heat is

lost?

85000 Joules

Page 25: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

A 15.8-gram piece of zinc increases in temperature

from 5.5°C to 6.9°C when 8.5 Joules of heat are added. What is the

specific heat of zinc?

0.38 J/g°C

Page 26: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

calorie (cal)Quantity of heat

needed to raise the temp of 1g of pure

water 1C

Page 27: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

How much heat is needed to increase the

temperature of 10g H2O from 35C to

45C?100 cal

Page 28: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

1000 calories = 1 Calorie

(Calorie is the kind on food labels, etc)

Page 29: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

1 calorie = 4.184 Joules

Page 30: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Calorimeter

An insulated chamber used to measure the

amount of heat absorbed or released

during a reaction

Page 31: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.
Page 32: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.
Page 33: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

When heat energy is added, the molecules move faster and

faster, increasing the temperature

What happens when the phase is not changing:

Page 34: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

When heat energy is added, instead of increasing the temperature (increasing the kinetic energy of the

molecules), the intermolecular bonds are broken,

changing the phase of the substance.

What happens during a phase change:

Page 35: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

PHASES OF WATER

Page 36: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat of Fusion (Hf)

Amount of heat necessary to convert a given

amount of a solid into a liquid

Q = mHf

Page 37: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.

Heat of Vaporization (Hv)Amount of heat necessary

to vaporize a given amount of liquid at its

boiling point

Q = mHv

Page 38: THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.