energy - calorimetry exercise 6

Solution

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

To obtain the change in enthalpy for the reaction below

Step 1 find the number of joules produced.
1kg of water increased in temperature by 6.7 degrees celsius
The amount of energy required to do this is given by the expression
heat capacity X mass of water X temperature change = 4.2 X 1000 X 6.7
= 28140 J or 28.4Kj.

Step 2) Mole of glucose added = 1.8 /180 = 0.01 mole

Step 3) Divide the amount of energy given out by the number of moles to get the enthalpy change.

28.40 / 0.01 = -2840Kj/mol

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

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Calorimetry exercise 6
A 1.8gram sample of glucose is burnt in a bomb calorimeter as pictured in the animation below. 1 kg of water was placed in the bomb calorimeter. C = 12, O = 16, H =1
The heat capacity of water is 4.2j/g/C. That is it takes 4.2 joules of energy to raise one gram of water by one degree Celsius.
C₆H₁₂O₆(s) + 6O₂(g) => 6CO₂(g) + 6H₂O(g)
a) Is the above reaction an exothermic or endothermic reaction? Explain. c) Calculate the enthalpy change of the reaction above. Solution
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