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) = 4.184 J (exact number)
– The energy needed to raise the temperature of 1 g of
water by 1˚C
1
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
H  H products  H reactants
– Exothermic: heat is released
– Endothermic: heat is absorbed
H  0
H  0
2
Identify each reaction as
Ex) exothermic
or En) endothermic.
A. N2 + 3H2
2NH3 + 22 kcal
B. CaCO3 + 133 kcal
C. 2SO2 + O2
CaO + CO2
2SO3 + heat
3
Calculation using Heat of Reaction
The reaction occurring in a cold pack is as follows:
2O
6.2 kcal  NH 4 NO3(s) H

 NH 4 NO3 (aq)
• 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?
1 mole NH 4 NO3 6.2 kcal absorbed
10. g NH4 NO3 

80.05 g NH 4 NO3 1 mole NH 4 NO3
Convert
to moles!
Moles  energy?
Energy is
a reactant!
 0.774516
 0.77 kcal absorbed
4
In the reaction
N2(g) + O2 (g)
kcal
2NO(g)
N2(g) + O2 (g) + 43.2 kcal
ΔH = 43.2
2NO(g)
If 15.0 g NO are produced, how many kcal were
absorbed?
5
Specific Heat (SH)
The amount of heat needed to raise the temperature of 1 g
heat
of a substance by 1 °C
SH 
grams  T
How much energy is needed to raise the temperature of 20.0 g
of iron by 14.5 °C?
6
• 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
Caloric Values:
food
Carbohydrate
Fat
(lipid)
Protein
4 kcal
1g
9 kcal
1g
4 kcal
1g
water
8
Entropy
• Entropy
– Entropy Describes degree of disorder
– Increasing disorder helps drive reactions
– Changes in disorder are indicated by ΔS
9
Gibbs Free Energy
• 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
10
States of Matter
Matter: anything that occupies space and has mass
Physical states:
• Solid
• Liquid
• Gas (vapor)
Shape?
Volume?
Movement of
particles?
Arrangement of particles?
Interaction between particles?
Attractive forces between particles hold substances together
• Dipole-dipole
Intermolecular forces
• Hydrogen bonds
• Dispersion
11
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 -78C.
• Takes place in frost-free refrigerators.
• Is used to prepare freeze-dried foods for longterm 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
Changes of State Equations
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
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