The heat energy change (Q) is something that can be calculated in the equation below:

Q=mc∆T

Where:

- m is the mass of the surroundings.
- c is the specific heat capacity.
- ∆T is the temperature change (final temperature - initial temperature)

100g of ethanol heated 250cm3 of water from 20◦C to 55◦C. Find the enthalpy change for this reaction. 250cm3 has a mass of 250g. Water has a specific heat capacity of 4.18 (unless it says otherwise). ∆T= 55-20=35

250 x 4.18 x 35= 36575J. It is an exothermic reaction so it becomes -36575J.

So now we find out the number of moles that reacted. One mole of ethanol has a mass of 46. 100/46= 2.17 moles. So for one mole of Ethanol we have to divide 36575 by 2.17 to get 16854.84j which in Kj is 16.85Kj.

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