Chapter 16.1 Notes
Energy and Heat
Heat Capacity and Specific Heat
Thermochemistry
• This chapter deals with
studying heat changes that
occur during chemical
reactions, which is defined as
thermochemistry.
This guy is enjoying the sun;
the sun is an example of thermochemistry in action.
A few thermo terms…
• Energy-the capacity to do work or
supply heat
• Chemical Potential Energy-stored
energy in the bonds of chemical
compounds
• Heat (q)-energy that transfers due
to a difference in temperature
(remember we already defined
temperature as the measure of
how much energy something has)
Exothermic reactions
• When heat is transferred from the
system to the surroundings
during a reaction, it is called
exothermic.
Combustion is
exothermic.
Only YOU can prevent
forest fires.
Endothermic reactions
• When heat is transferred from the
surroundings to the system
during a reaction, it is called
endothermic.
Measuring Heat
• There are two units of measurement
we will discuss when calculating heat
(q).
• calories- a calorie is the amount of
heat it takes to raise one gram of
water by one degree celsius
• (note: this is different from a food
Calorie, which is actually 1 kilocalorie)
• Joules (SI)- 4.184 Joules = 1 calorie
Heat Capacity
• How much heat it takes to raise the
temperature of an object by 1oC is
called its heat capacity.
• What variables affect heat capacity?
– Amount of substance
– Type of substance
Specific heat capacity (a.k.a.) specific heat
• Scientists do not generally like to
compare heat capacities, because
there are two different variables, SO
they compare 1g of substances to
come up with the specific heat
capacity.
As you can see, scientists
like Einstein do not like two variables!
Specific heat
• The amount of energy required to
raise the temperature of 1g of
substance by 1oC is its specific heat.
• The formula for specific heat is:
q=(m)(Cp)(DT)
Heat
=
mass x specific heat x change in temp.
Specific heat, cont.d
• When solved for C, you get:
q__
Cp =
(m)(DT)
Practice Problem #1
• When 435J of heat is added to 3.4g of
olive oil, it raises the temperature from
21oC to 85oC. What is the specific
heat of olive oil?
Practice Problem #2
• A 1.55g piece of stainless steel
absorbs 141J of heat when its
temperature is increased by
178oC. What is the specific heat
of the stainless steel?
Mr. Huggins’s morning coffee increases the temperature
of his travel mug. Chemistry in action!
Practice Problem #3
• How much heat is lost when a 250.0g
sample of mercury’s temperature is
lowered by 52oC?
CHg=0.14 J/goC
Mercury was once used in the hat
making industry, but the vapors
reacted with employee nervous
systems and drove them insane.
Hence the phrase, mad as a hatter.