calorimetry The measurement of heat in a reaction is called calorimetry. Through this, we find that different substance require different amounts of heat to change their temperature.

The specific heat of a substance is the amount of heat energy required to raise the temperature of one unit of mass of that substance by one unit of temperature.

Let’s define some variables… Q = heat lost or gained m = mass c = specific heat t i & t f = initial & final temperature

We can now write our formula as Q = m c  t or Q = m c (t f - t i ) First, let’s do this...  t = (t f - t i )

Let’s define some variables… Q = heat lost or gained m = mass c = specific heat t i & t f = initial & final temperature

The energy of the universe is constant! This means that when one object looses energy another object in the universe gains energy. This can be stated mathematically: -Q lost = Q gained

-Q lost = Q gained Note the minus sign The minus means that energy is lost. The energy of the object has decreased. Some other place in the universe gains an equal amount of energy represented by the + sign.

Exothermic – energy is lost by an object (represented by -) Endothermic – energy is gained by an object (represented by +)

To calculate these energy changes consider this situation: 100 grams of water is heated from 25 ¡ C to 50 ¡ C. How much energy is required to do this? Is this process exothermic or endothermic?

This process is endothermic! Energy is being added to the water. The next question is: What is the specific heat for water? The answer is: J/g-  C

Now we can calculate the energy Q=mcèt èt=(t f -t i )=(50- 25)¡C=25¡C Q=100 g (4.184 J/g- ¡C)(25¡C) Q= J = 10.5 kJ