Ch 16
Reaction Energy
 Standard:
–7.d. Students know how to solve
problems involving heat flow an
temperature changes, using known
values of specific heat.
 Objective:
–We will define heat, give its units,
and perform specific-heat
calculations.
Thermochemistry
 Thermochemistry:
the study of the
transfer of energy as heat that occurs
during chemical reactions and changes in
state.
 Heat: q, is energy transferred from one
object to another because of a
temperature difference between them.
 Heat always flows from a warmer object
to a cooler object and will continue to
flow until they are in equilibrium.
 Endothermic
Process: one that
absorbs heat from the
surroundings (+q).
 Exothermic Process: one that
releases heat to it’s surroundings
(-q).
 Calorimeter: the insulated device
used to measure the absorption or
release of heat in chemical or
physical processes.
Specific Heat
 Heat
flow is measure in joules (J).
 One joule of heat raises the
temperature of 1g of pure water
0.2390°C
 Specific Heat: the amount of heat
needed to increase the temp of 1 g
of the substance 1°C.
– The specific heat is the heat capacity of an
object divided by its mass in grams.
Calculating Specific Heat (C)
 Divide
the heat input, q (Joules) by the
temperature change, ΔT (°C) times the
mass of the substance, m (g).
C=
q
=
heat
m x ΔT mass x change in temp
Example
 The
temperature of a 95.4 g piece
of copper increases from 25.0°C to
48.0°C when the copper absorbs
849 J of heat. What is the specific
heat, C, of copper?
q = 849 J m = 95.4g
ΔT = (48.0°C -25.0°C)=23.0°C
C=
q
=
849 J
m x ΔT
95.4 g x 23.0°C
C = 0.387 J/(g x °C)
Example 2
 How
much heat, q, is required to
raise the temperature of 400.0 g of
silver 45°C? The specific heat of
silver is 0.24 J/(g x °C).
ΔT = 45°C
m = 400.0 g
C= 0.24 J/(g x °C)
q = C x m x ΔT
q = 0.24 J/(g x °C) x 400.0 g x 45°C
q = 4320 J
 Table
Homework Notes
1 is on page 533.
 Kelvin and Celsius are interchangeable
because they are on the same scale.
 cp is the same as C
 #7 solve for q
 #8 solve for ΔT, add that to 20°C
and then convert to Kelvin.
 ΔT = q /(C x m)
 #9 solve for C
 #10 change mol to g and solve for C
Chapter 17
Reaction Kinetics
Ch 17.1
Reaction Kinetics
 Standard:
–8.a. Students know the rate of
reaction is the decrease in
concentration of reactants or the
increase in concentration of
products with time.
 Objective:
–We will use the collision theory to
interpret chemical reactions and
define activated complex. We will
draw energy diagrams.
Collision Theory
 Collision
Theory: atoms, ions, and
molecules can react to form
products when they collide with
each other, provided that the
colliding particles have enough
kinetic energy.
 Think about two balls of clay. If you
throw them together gently, they won’t
stick together, but if there is enough
energy, they will stick together.
 Rate:
a measure of the speed of
any change that occurs within an
interval of time.
 In chemistry, the rate of chemical
change or the reaction rate is usually
expressed as the amount of reactant
changing per unit time.
 Activation Energy: the minimum
energy that colliding particles must
have in order to react.
 Activated
Complex: an unstable
arrangement of atoms that forms
momentarily at the peak of the
activation-energy barrier.
 This is also called the Transition
Rate.
Sample Problem A
page 566
and
Practice Problem 2
page 567
Ch 17.2
 Standard:
–8.b. Students know how reaction rates
depend on such factors as
concentration, temperature and
pressure.
–8.c. Students know the role a catalyst
plays in increasing the reaction rate.
 Objective:
–We will discuss the factors that
influence reaction rate and define a
catalyst.
Factors Affecting Reaction Rates
 The
rate of a chemical reaction
depends upon temperature,
concentration, particle size, and
the use of a catalyst.
TEMPERATURE
 Raising the temperature speeds up
the reaction and lowering the
temperature slows down the
reaction.
CONCENTRATION
 The higher the concentration, the
more likely collisions will take
place, which increases the reaction
rate.
PARTICLE SIZE
 The smaller the particle size, the
more surface area, which
increases the reaction rate.
CATALYSTS
 Adding a catalyst will increase the
rate of reaction, in some cases,
better than increasing the
temperature.
 Inhibitor: a substance that
interferes with the action of a
catalyst.
– These will slow down or even stop a
reaction
Nature of Reactants
 The nature of the reactants involved
in the chemical reaction also play a
part. But just remember the first
four.