Calculating Heat

To calculate heat, you use the formula Q=mcAt (A is representing delta)

Q is heat in Joules
m is mass in grams
c is specific heat in J/g degrees C
At is change in temperature

Example 1: Calculate the amount of energy in joules required to heat 454 grams of water from 5.4C to 98.6C:

Q=?   m=454g    At=93.2  Ti=5.4   Tf=98.6   c=4.184
454(4.184)(98.6-5.4)= 1.77x10^5 J OR 177 kJ

Example 2: A 2.6g sample of metal requires 15.6J of energy to change its temperature from 21C to 24C. What's the identity of the metal?

m=2.6g   Q=15.6J   Ti=21   Tf=34   c=?
15.6=2.6(c)(34-21)
C=.46 J/gC OR Iron

Temperature and Heat

The Kinetic Molecular theory states that as a substance is heated, molecules gain energy. However, we cannot measure the amount of energy in the form of heat a substance contains, but we can measure the flow of heat energy. This is always from a warm to cold body until the temperature equalizes. This change is used to measure heat flow.

Exothermic: If there's an output of energy out of the system, then the system is losing energy.

Endothermic: If there's an input of energy into the system, then the system is gaining energy.

Endothermic vs. Exothermic

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