Ch 16-17 Notes - Hemet High School
Download
Report
Transcript Ch 16-17 Notes - Hemet High School
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.