Chapter 16
Chemistry
 Energy
is the ability to do work or produce heat
 Energy
stored in a substance because of its
composition
 Calorie
– amount of heat needed to raise the
temperature of 1g of water 1oC
 Calorie
 Joule
= 1000 calories
= SI unit of energy (4.18 J = 1 calorie)
 The
breakfast shown in the photograph contains 230
Calories. How much energy in joules will this
healthy breakfast supply?
 230
Calories x 1000 = 230,000 calories
 230,000 calories x 4.18 Joules = 9.6 x 105 Joules
464 KJ per
serving
 Amount
of heat required to raise the
temperature of 1g of any substance 1oC
 The
specific heat of water is 4.184J/g.oC

In the construction of bridges and skyscrapers,
gaps must be left between adjoining steel beams
to allow for the expansion and contraction of the
metal due to heating and cooling. The
temperature of a sample of iron with a mass of
10.0g changed from 50.4oC to 25oC with the
release of 114J heat. What is the specific heat of
iron?

Formula: Q = mcDT
m = mass
c = specific heat
Dt = change in temperature
Q = Heat (energy)
 Insulated
device used to determine heat changes
A
piece of metal with a mass of 4.68g
absorbs 256J of heat when its temperature
increases by 141oC. What is the specific heat
of the metal?
 Can
you identify the metal? Where do you
think you might find this kind of information?
Calculate the Difference!
 What
is the formula?
 Find
specific heat if a 8.5g object releases
113 J of heat energy with a temperature
change of 24 degrees Celsius.
 Find
how much heat is released if a 12g
object with a specific heat of .31 changes
from 55oC to 25oC.
 System
= specific part of universe that contains
the reaction
 Surroundings
 Universe
= everything else in the
universe – the reaction
is the sum of the system and its
surroundings
 (H)
is the heat content of a system at
constant pressure
 It
is the heat absorbed or released during a
chemical reaction
a reaction releases heat, DH is negative
 If a reaction absorbs heat, DH is positive
 If
 In
a chemical reaction, solids can be heated to
the point where the molecules holding their
bonds together break apart and form a liquid.
The most common example is solid ice turning
into liquid water. This process is better known
as melting, or heat of fusion, and results in the
molecules within the substance becoming more
chaotic
q = mHf
How much heat is required to melt 4 kg of
ice at 0 ºC? Remember there is no ΔT in a
phase change.
q = mHv
How much heat is required to turn 12 kg of
water at 100 ºC into steam at the same
temperature? Again, there is no ΔT in a
phase change.
Where are the phase changes? How do you recognize them? Which is which?
 (s)
is the measure of disorder or randomness
of the particles that make up a system
A
system tends to go to a more disordered
state or increased entropy
 DG
is the energy available to do work
 DG
= DH –TDS
 Calculate
Gibbs free energy if DH = - 6760J ,
DS = -197J/K , and the temperature is 298K.
 If
a reaction has a –DG, then the reaction will
be spontaneous ( it will occur without
outside intervention)
ADP + Pi ATP
ΔG° = +30 kJ mol–1
C6H12O6 + 2 ADP → 2 CH3CH(OH)COOH ΔG° = –218 kJ mol–1
Calculate DG using DG = DH - TDS. Also, for
each question, tell whether or not the
reaction will be spontaneous.
a) CH3OH(l) + 1½ O2(g) CO2(g) + 2 H2O(g)
H = -638.4 kJ S = 156.9 J / K
b) 2 NO2(g) N2O4(g)
H = - 57.2 kJ S = -175.9 J / K
 Collision
Theory
 Nature
of Reactants
 Concentration