Energy• Energy: the ability to do work

– Potential Energy: stored energy– Kinetic Energy: energy of motion

• Heat:– Energy associated with motion of particles– Units:

• joule (J)

• kilojoule (kJ)

• calorie (cal)– The energy needed to raise the temperature of 1

g of water by 1˚C

1

= 4.184 J

(exact number)

Energy in Chemical Reactions• Activation energy: energy needed for reaction to

occur– “hill” we must climb over

• Heat of reaction: – Amount of heat absorbed or released during a reaction

– Exothermic: heat is released– Endothermic: heat is absorbed 2

reactantsproducts HHH 0H0H

Identify each reaction as

Ex) exothermic or En) endothermic.

A. N2 + 3H2 2NH3 + 22 kcal

B. CaCO3 + 133 kcal CaO + CO2

C. 2SO2 + O2 2SO3 + heat

3

Calculation using Heat of Reaction

The reaction occurring in a cold pack is as follows:

4

(aq)(s) NONH NONHkcal 6.2 34OH

342

• Is this reaction exothermic or endothermic?

• If 10. g of ammonium nitrate is contained in the pack, how much heat can be absorbed or released if it reacts completely?

34NONH g 10.34

34

NONH g 50.80

NONH mole 1

Convert to moles!

34NONH mole 1

absorbed kcal 6.2

Moles energy?Energy is a

reactant!

774516.0

absorbed kcal 77.0

In the reaction

N2(g) + O2 (g) 2NO(g) ΔH = 43.2 kcal

N2(g) + O2 (g) + 43.2 kcal 2NO(g)

If 15.0 g NO are produced, how many kcal wereabsorbed?

5

Specific Heat (SH)The amount of heat needed to raise the temperature

of 1 g of a substance by 1 °C

6

Tgrams

heatSH

How much energy is needed to raise the temperature of 20.0 g of iron by 14.5 °C?

• A hot-water bottle contains 750 g of water at 65°C. If the water cools to body temperature (37°C), how many calories of heat could be transferred to sore muscles?

7

Energy and Nutrition & Calculation

• Nutritional Calorie = Cal= 1 kcal = 1000 cal

8

g 1

kcal 4

g 1

kcal 9

g 1

kcal 4

Carbohydrate

Fat(lipid)

Protein

Caloric Values:

food

water

Entropy

• Entropy– Entropy Describes degree of disorder– Increasing disorder helps drive reactions– Changes in disorder are indicated by ΔS

9

Gibbs Free Energy

10

• Used to determine if reaction is spontaneous or not• Takes into consideration heat of reaction,

temperature and entropy• Negative ΔG is spontaneous and positive ΔG is

nonspontaneous

States of Matter

Matter: anything that occupies space and has mass

Physical states:• Solid• Liquid• Gas (vapor)

11

Shape?

Volume?

Arrangement of particles?

Interaction between particles?

Movement of particles?

Attractive forces between particles hold substances together

• Dipole-dipole• Hydrogen bonds• Dispersion

Intermolecular forces

Intermolecular Forces• Dipole-dipole:

– Polar molecules act like magnets– Ex. HCl and HCl

• Hydrogen bonds:– Strongest dipole-dipole interaction– Only occur between:

• Hydrogen and…

• Nitrogen, Oxygen or Fluorine

– Ex. Water

• Dispersion:– Very weak force– Nonpolar molecules (have brief polar moment)

12

Changes of State

13

Melting/Freezing

A substance • Is melting when it changes from a solid to

a liquid.• Is freezing when it changes from a liquid

to a solid.• Such as water has a freezing (melting)

point of 0°C.

14

Sublimation

Sublimation• Occurs when a solid changes directly to a

gas.• Is typical of dry ice, which sublimes at -

78C.• Takes place in frost-free refrigerators.• Is used to prepare freeze-dried foods for

long-term storage.

15

Evaporation/Condensation

Water• Evaporates when molecules on the surface gain

sufficient energy to form a gas.• Condenses when gas molecules lose energy and form a

liquid.

At boiling, • All the water molecules acquire enough energy to form a

gas.• Bubbles appear throughout the liquid.

16

The heat of fusion • Is the amount of heat released when 1

gram of liquid freezes (at its freezing point).

• Is the amount of heat needed to melt 1 gram of a solid (at its melting point).

• For water (at 0°C) is 80. cal 1 g water

17

Changes of State Equations

Changes of State Equations

The heat of vaporization is the amount of heat• Absorbed to vaporize 1 g of a liquid to gas at the

boiling point.• Released when 1 g of a gas condenses to liquid at

the boiling point.

Boiling Point of Water = 100°C

Heat of Vaporization (water) = 540 cal

1 g water= 540

cal / g 18

Heating and Cooling Curves

Ice Cream

20