Download Chapter 11 Notes - Net Start Class

Chapter 11 Notes
Energy and Heat
Heat Capacity and Specific Heat
• Thermochemistry is the study
of heat changes that occur
during chemical reactions.
• Energy is the capacity to do work
or supply heat
• Chemical Potential Energy is
stored energy in the bonds of
chemical compounds
• Heat (q) is the energy that
transfers due to a difference in
temperature
(remember temperature is the
measure of how much energy
something has)
• Exothermic reactions occur when
heat is transferred from the
system to the surroundings during
a reaction.
• Endothermic reactions occur
when heat is transferred from the
surroundings to the system during
a reaction.
Measuring Heat
• There are two units of heat (q)
measurement .
• calorie - 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: 4.184 Joules = 1 calorie
• Heat capacity is how much heat it
takes to raise the temperature of an
object by 1oC.
• The two variables affect heat capacity
are:
–Amount of substance
–Type of substance
• Scientists do not generally like to
compare heat capacities, because
there are two different variables, SO
they compared 1g of substances to
come up with the specific heat
capacity which is also known as
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 Formula
• When solved for Cp, you get:
Cp =
q__
(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?
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