Energy
Energy is defined as capacity to do work
Work is done when a force is used to change the position or motion of
matter.
Potential Energy: energy due to position
Kinetic Energy: energy of motion
Ways that energy can be expressed (forms of energy)
S - Sound
A – Atomic (nuclear)
C - Chemical
H - Heat
E - Electrical
M - Mechanical
L - Light
Law of Conservation of Energy:
Energy can not be created or destroyed, only transferred (it can only
change form). Example: Battery – Chemical  electrical  sound in radio
Exothermic: Release of heat energy
Endothermic: Absorption of heat energy
Heat - Always goes from high temperature to low temperature
Hot Pack-Heat flows from the pack to your body
Cold Pack-Heat flows from your body to the pack
Measurement of Energy:
Thermometer: a device used to measure the temperature of a system
Temperature is the average kinetic energy of a substance.
NOTE: a) Heat is NOT in the definition
b) Average is of all the particles in the sample.
Thermometry:
Celsius and Kelvin are the two scientific temperature scales.
Boiling Point: temperature at which liquid becomes a gas
Freezing Point: temperature at which liquid becomes solid
For water at Standard Pressure (1 atm or 101.3kPa)
Boiling Point is 100C or 373 K
Freezing Point is 0C or 273 K
To convert form one temperature scale to the other:
C to K C + 273 = K
K to C K – 273 = C
Absolute Zero: The theoretical temperature at which all molecular motion
ceases. (0K or -273C)
STP stands for: Standard temperature (273 K) and pressure (1 atm)
This information can be found on Table A
Calorimetry: Process of measuring heat exchange during a reaction
Calorimeter: device that uses changes in temperature of water to
measure heat exchange during a reaction.
Calorie (cal): a unit of heat energy – amount of heat needed to
raise the temperature of 1g of water 1C.
Joule (J): a unit of heat energy 4.18 are needed to raise the
temperature of 1g of water 1C
Specific Heat (C): amount of heat energy needed to raise the
temperature of 1g of any substance by 1C.
For Water: Specific Heat = 4.18J/g K or 1 cal/g K
FORMULA: q = mCT
Where:
Table T
q = heat
m = mass
C = specific heat
T = change in temperature
Example:
How many joules of heat are absorbed by 45g of water when the
temperature of that water is raised from 293K to 323K?
Step 1: q = mCT
write the formula
Step 2: q =
identify the variables
m=
C=
T =
Step 3: q =
plug into formula with units
Step 4: q =
solve (don’t forget units!)
A reaction chamber inside a calorimeter contains 245g of water at 23C.
After the reaction, the temperature of the water is at 28C. How many
joules were released during the reaction?
Step 1:
Step 2:
Step 3:
Step 4:
If the amount of energy being calculated occurs during a phase change you must use
one of the two following formulas:
q=mHf
or
q=mHv
q=heat
q=heat
m=mass
m=mass
Hf=heat of fusion
Hv=heat of vaporization
*this is for
*this is for
solid/liquid
liquid/gas
How much energy is required to completely melt 25g of ice?
How much energy is absorbed as 10g of water turns to steam?