Determining the Heat Lost/Gained by an Object


Heat transfer, and the three ways in which heat transfer occurs, has been discussed in previous pages. However, there is a general equation that just describes the heat that an object can hold, which is independent of the method of heat transfer that the object goes through. When an object changes from one temperature to another, the object either gains or loses heat. Another equation is necessary to describe this effect. It is as follows:

Q = m Cp D T

Each symbol stands for a different quantity.

Example: Joules (J), kilojoules (kJ), ergs, calories (cal), kilocalories (kcal), Newton-meters (Nm), or BTUís

  • m: mass of the object

Example: grams (g), kilograms (kg), milligrams (mg)

  • Cp: heat capacity of an object

(Heat is energy transferred between two objects because of a temperature difference between them and capacity is the maximum amount that something can hold. Therefore heat capacity is the maximum amount of heat that an object can hold.)

    • Units: units of energy/(mass*temperature)

Example: J/(kg*K), BTU/(lb* ° F), cal/(g*° C)

  • D : Greek letter called "delta" that represents the words "change in."

(When the symbol D is used, it refers to subtracting the beginning value from the final value of the symbol following the D .)

    • Units: units of temperature

Example: ° C, ° F, K, R

Therefore, returning to the equation,

Q = mCpD T

It was shown that the amount of heat gained or lost by an object is equal to the objectís mass times its heat capacity times the change in temperature the object undergoes.

Proceed to An Example Using this System
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[Introduction | Kinetics | Heat Transfer | Mass Transfer | Bibliography]

This project was funded in part by the National Science Foundation and is advised by Dr. Masel and Dr. Blowers at the University of Illinois.

© 2007 Arizona Board of Regents for The University of Arizona