Untitled - Kelly Walsh High School

Thermochemistry 99
Quick Tip
Don’t Forget!
or released during the chemical or physical change is q, and is proportional to
the change in temperature of the system. This system has a heat capacity, which
is the quantity of heat needed to change the temperature 1 K. It has the form:
Heat capacity q/T
The heat capacity most commonly has units of J/K. The specific heat capacity
(or specific heat) (c), is the quantity of heat needed to raise the temperature of
1 g of the substance 1 K:
c q/(mass)(T) or q (c)(mass)(T)
The specific heat capacity commonly has units of J/gK. The specific heat capacity
of water is 4.18 J/gK. If we have the specific heat capacity, the mass, and the
change of temperature, it is possible to determine the amount of energy
absorbed or released (q).
The specific heat capacity of water is necessary to solve many problems.
However, when reading the problem, it is often not apparent that you must use
this value. If the problem mentions water, its specific heat capacity will often be
part of the solution to the problem.
Don’t mix energy units, J and cal; always use appropriate conversions.
Another related quantity is the molar heat capacity (C), the amount of heat
needed to change the temperature of 1 mol of a substance 1 K.
Calorimetry involves the use of a laboratory instrument called a calorimeter.
Two types of calorimeters are commonly used, a simple coffee-cup calorimeter
and a more sophisticated bomb calorimeter. In both, we carry out a reaction
with known amounts of reactants and the change in temperature is measured.
Check your textbook for pictures of one or both of these.