HEAT IS ENERGY

On the last page, we saw that a little bit of hot water isn't as good as a lot of warm water when you need to heat something up.
So it is clear that when considering the amount of energy in heating objects, we must consider the amount of matter (mass) involved.
What else must we consider?
 

  • the amount of temperature change
  • the nature of the substance(s) involved


    • To find the joules released or absorbed in a temperature change, we use this equation:

    Q=mcDT

    "Q" is in joules if...

  • mass is in Kg
  • c is in joules/Kg°C
  • DT is in degrees Celsius or Kelvin


    • The "c" is a constant called specific heat that depends on what substance you are referring to.  For example, Lead is very easy to heat or cool (c = 128 j/Kg°C) and water is very hard to heat or cool (c = 4190 j/Kg°C)


    In the lab, a scientist requires 1950J of heat to raise the temperature of a .5Kg piece of copper from 100°C to 110°C.  What is the specific heat of copper?

    since Q=mcDT, then c=Q/mDT

    inserting numbers...

    c = 1950J/(.5Kg * 10°C) = 390 J/Kg°C