1 of 12

5.2 CALORIMETRY

2 of 12

SPECIFIC HEAT CAPACITY (c)

… the quantity of thermal

energy required to raise the

temperature of 1 g of a

substance by 1 C.

​

… measured in J/(g* C)

​

It takes a lot more energy to heat 1 g of water than it does to heat 1 g of sand!

3 of 12

4 of 12

CALORIMETRY

Consider heating water on a

gas stove:

​

Thermal energy is transferred from the natural gas to the water. The kinetic energy of the water molecules increases. The average kinetic energy (temperature) of the water increases.

​

Calorimetry is the experimental process of measuring the thermal energy change in a chemical or physical change.

5 of 12

WHAT IS A CALORIMETER?

A calorimeter allows us to measure thermal energy changes in a chemical or physical change.

​

A bomb calorimeter is tightly sealed and prevents any gas from escaping, which causes pressure changes based on whether or not gases are being produced or consumed.

6 of 12

7 of 12

BEFORE WE BEGIN CALCULATIONS, WE MUST MAKE SOME ASSUMPTIONS...

  • Any thermal energy transferred from the calorimeter to the surroundings is negligible

​

  • Any thermal energy absorbed by the calorimeter is negligible

​

  • All dilute, aqueous solutions have the same density (1.00 g/mL) and specific heat capacity (4.18 J/g* C) as water

8 of 12

WHAT IS q?

The total amount of thermal energy absorbed or released by a chemical system is given the symbol q.

​

q depends on…

1) the mass of the substance

2) the specific heat capacity of the substance

3) the temperature change

9 of 12

m = the mass of the substance

c = the specific heat capacity

T = the temperature change (Tfinal - Tinitial)

​

The value of q has two parts:

1) the magnitude (how much energy involved)

2) the sign (direction of energy transfer)

10 of 12

MORE ON q

IF q IS NEGATIVE...

IF q IS POSITIVE...

  • the system transfers thermal energy to the surroundings
  • temperature of water increases
  • change is exothermic
  • thermal energy is absorbed into the system
  • temperature of water decreases
  • change is endothermic

11 of 12

We will do three sample problems on the chalkboard, old school style!

12 of 12

HOMEWORK

p. 297 #1-3

​