Solution
The reaction is an endothermic
reaction. Heat is absorbed as the temperature decreases.
The calibration factor of the calorimeter is given by the expression below.
Obtain the amount of energy absorbed from 1.01 grams of potassium nitrate
Calibration factor X change in temperature = 1159.7 X 0.672 = 0.779KJ
The enthalpy change is energy/mol
SO!
Step 1) Mole of potassium nitrate added = 1.01 /101 = 0.01 mole
Step 2) Divide the amount of energy by the number of mole of potassium nitrate.
0.779 / 0.01 = 77.9Kj/mol
Note how the enthalpy change has a positive sign. This indicates an endothermic reaction (heat absorbed from the surroundings).
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Calorimetry
exercise 2 |
A current of 1.70 A was passed through the heating coil of a calorimeter for 50.5 seconds at a potential difference of 6.18 V. The temperature increased from 20.340 to 20.796 degrees Celsius. N =14, C = 12, O = 16, H =1, K =39 |
1.01 grams of potassium nitrate was dissolved in a calorimeter and the temperature dropped from 20.34 to 19.668. a) Is this an exothermic or endothermic reaction? Explain. b) Write the equation for the reaction. c) Calculate the enthalpy change of the equation in b).
Solution |