Heat

Heat

•Temperature and heat are not the same thing

•We measure how hot or cold something is by temperature

•There are three common scales to measure temperature

Heat

•The scale we are the most familiar with is the Fahrenheit scale

•Water freezes at 32 degrees Fahrenheit

•Water boils at 212 degrees Fahrenheit

Heat

•Another temperature scale is the Celsius temperature scale

•Water freezes at 0 degrees Celsius

•Water boils at 100 degrees Celsius

Heat

•The temperature scale that scientists use is the Kelvin scale

•Water freezes at 273.15 Kelvin

•Water boils at 373.15 Kelvin

•Kelvin is the SI unit for temperature

Heat•To convert from Kelvin to Celsius

simply subtract 273.15

•To convert from Celsius to Kelvin simply add 273.15

•All temperatures must be in Kelvin unless you are taking the change in temperature, then Celsius is okay, since a degree is the same increment for both

Heat

•To convert from Fahrenheit to Celsius

•°C = (5/9)(°F - 32)

•To convert from Celsius to Fahrenheit

•°F = (9/5)°C + 32

Heat

•Temperature is a measure of the average kinetic energy (KE) an object contains

•Heat is what we call a transfer of energy from one object to another

•Energy always flows from a warmer object to a colder one

Heat

•A warmer object will continue to transfer energy to a colder one until equilibrium is reached

•The warmer object always gives up energy to a colder one

•Scientists prefer to call heat internal energy

Heat

•Different substances absorb heat (energy) at different rates

•The rate at which this substance absorbs heat is called it specific heat capacity

•There is an equation to determine how much energy is absorbed

Heat•Q = mCΔT

•Q - the amount of energy (measured in Joules)

•m - the mass of the substance (measured in kilograms)

•C - the specific heat capacity (measured in Joules per kilogram Kelvin

Heat

•ΔT - the change in temperature (measured in Kelvin or Celsius)

•Again we can use Kelvin or Celsius since we are taking the difference in temperature

Heat

•Water has a very high specific capacity which gives water its unique properties

•It can absorb a tremendous amount of energy without a significant temperature change

Heat

•The high specific heat of water is why coastal areas don’t vary in temperature too much

•The large amount of water on Earth keeps us from having drastic temperature changes between day and night and summer and winter

Heat

•Water can absorb 4180 J of energy per kilogram and only increase temperature by one degree

•Water can also release 4180 J of energy per kilogram and only decrease temperature by one degree

Heat

•Example 1:

•How much thermal energy does it take to change 2 kg of water from room temperature (20°C) to boiling (100°C)?