Calculations Involving Heat
Temperature (T)- the measure of the average kinetic energy of particles that make up a
substance in a system. Temperature is measured by °C or Kelvin.
Kelvin= Temperature in °C + 273.15K
Change in temperature is an indication of change in kinetic energy: ΔT= Tf - Ti
Where Tf= Final Temperature and Ti=initial temperature
Heat (q)- refers to the transfer of kinetic energy between objects with different temperatures.
Heat is also measured by joules. When energy is transferred as heat:
q system = - q surroundings
When substances with different temperature come in contact, kinetic energy is transferred as
heat from the particles of the warmer substance to the particles of the cooler substance. Mass
is also directly related to heat transfer. Different substances have a different ability to absorb
and give off heat.
Specific heat capacity (c) - the quantity of energy in joules that is required to change one gram
of the substance by one degree Celsius (J/g∙°C). The specific heat capacity lets us know how
well a substance can store energy. The higher the specific heat capacity, the more energy a
substance can absorb and release.
Example: water has a specific heat capacity of 4.184 J/g∙°C (*See table 16.1 in textbook)
To calculate heat transfer or change in kinetic energy, we have to take into account a
substances heat capacity, its mass and the change in temperature. Using the following
equation, we can find the heat that a substance has absorbed or given off.
q= mcΔT q = heat (J) , m=mass (g), ΔT= Tf - Ti (0 C)
Try This: Calculate the missing values.
Substance
Heat
Exchanged (J)
Water
+1530
Mass
(g)
Specific
heat (J / g ·
oC)
T (oC)
Initial
Final
Temperature Temperature
(oC)
o
( C)
20.0
23.2
Aluminum
+3600
Steam
-1500
Mercury
+825
14
95
26
20
14
48
-25
152
116
42.0