Energy
• Energy – the ability to do work
•
• Kinetic – energy of motion, anything
that moves has kinetic energy.
•
K.E. = 1/2mv2
• Potential – is stored energy, chemical
or mechanical
• Law of Conservation of energy or law of
conservation of matter and energy
• Matter and energy can not be created
or destroyed; it can only be converted
from
• One form to another. E = mc2
Heat (q) is a measure of energy, in the metric system the
unit of measure is a calorie.
A calorie is the amount of heat required to raise the
temperature of one gram of water one degree Celsius.
In the SI system the unit is a joule.
1 calorie = 4.184J
So heat is a measure of the amount energy while
temperature is more of an Indication of the direction of flow
of the energy. It always flows from the object
With the higher temperature to the lower one.
Specific heat
• Specific Heat – the amount of energy
needed to raise one gram of the material
one degree Celsius.
For water its
4.184j/(g.°C)
or 1c/(g.°C)
• Calculating heat absorbed
• q = c x m x ∆T
some times
∆H is used in place of q
• q is the heat change , c is the specific
heat, m is the mass of the sample and
∆T is the change in temperature of the
sample.
• Example
How much energy is required to warm
250.grams of water from 20.0°C to
100.°C for a cup of coffee?
Q = 4.184j/g.°C x 250.grams x 80.0°C
Q = 83680 → 83700joules (to 3 sig figs )
• You should be able to solve for any of the
variables in the equation given the other
three values or a way to find them.
C = q / m x ΔT
m = q / c x ΔT
ΔT = q / c x m
Q=
m x ∆T
c x m x ∆T
m x ∆T
Calorimetry - a method of determining the heat
change of a chemical or physicl change.
Calorimeter – well insulated container used in
calorimetry.
Reactions can be endothermic, absorb energy or
exothermic which release energy.
(Hypothermia )
Phase change graph
Phase change graph and energies
• Hf = 334j/g
Hvap = 2260j/g
sph ice = 2.03j/g
• sph liq = 4.184j/g
sph steam = 2.01j/g