energy - simple calorimetry - specific heat of water

Solution

The reaction is an exothermic reaction. Heat is given off.

The calibration factor of the calorimeter is given by the expression below.

Obtain the amount of energy released from 0.02134 grams of ethene burnt in oxygen according the equation below

Calibration factor X change in temperature = 759.6 X 1.42 = 1.078KJ

The enthalpy change is energy/mol

SO!

Step 1) Mole of ethene added = 0.02134 /28 = 0.00076 mole

Step 2) Divide the amount of energy by the number of mole of ethene.

1.078 / 0.00076 = -1418.42Kj/mol

Note how the enthalpy change has a negative sign. This indicates an exothermic reaction (heat given out).

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Simple calorimetry

Specific heat of water

4.18J/g/C°

We can use the specific heat of water to make calculations on energy change during chemical reactions. Water has a specific heat capacity of 4.18J/g/C°. This means that 4.18 joules of energy must be supplied to every gram of water to raise the temperature by 1 degree Celsius.

Look at the experiment above and calculate the amount of energy, in joules per gram of jelly bean.

Step 1. Calculate the mass loss of the jelly bean. This is the amount that was burnt to release its energy.
initital mass - final mass = 5.69 - 3.89 = 1.80 grams

Step 2 Calculate the temperature rise

initial -final = 28 - 23 =5°C

Step 3 calculate the amount of energy released
energy released = 4.18 X mass of water X temperature rise.
energy released = 4.18 X 60 X 5 = 1254Joules or 1.25KJ

Step 4 calculate the amount of energy per gram released by the jelly bean
energy per gram = 1254 / 1.8 = 696.67Joules/gram