Question

The complete combustion of salicylic acid releases 21.90 kJ of energy per gram of salicylic acid....

The complete combustion of salicylic acid releases 21.90 kJ of energy per gram of salicylic acid. In a particular bomb calorimeter (initially at room temperature), the combustion of 0.2476 g of salicylic acid, in the presence of excess oxygen, causes the temperature of the calorimeter to rise by 2.74 °C. When a 0.3522-g sample of an unknown organic substance is similarly burned in the same calorimeter, the temperature rises by 3.88 °C. What is the energy of combustion per unit mass of the unknown substance?

Homework Answers

Answer #1

First, determine the calorimeter constant using the known substance.
The calorimeter constant incorporates the specific heat of the calorimeter fluid (likely water) and its mass.

Heat = 21.90 kJ/g * 0.2476 g = 5.4224 kJ

5.4224 kJ = c∆T
5.4224 kJ = c(2.74°C)

c = 1.979 kJ/°C

Now, we use the same calorimeter constant on our unknown substance.

Heat = 1.979 kJ/°C * 3.88°C = 7.678 kJ

Now, find the heat of combustion per gram:

7.678 kJ / 0.3522 g = 21.80 kJ/g

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