Question

Ethanol (C2H5OH) melts at -114 degrees Celsius. The enthalpy of fusion is 5.02 kj/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-K, respectively. How much heat (kJ) is needed to convert 25.0 g of solid ethanol at -135 degrees Celsius to liquid ethanol at -50 degrees Celsius?

Answer 1

The easiest way to do these problems is in parts and you need three formulas to do it.
q at a phase change; i.e., solid to liquid or liquid to gas.
For solid to liquid (melting point) it is
q = mass solid x heat fusion.

For liquid to gas (boiling point) it is
q = mass liquid x heat vaporization.

All other points you have "within" a phase; i.e., change temperature from a lower point to a higher point but solid all the way, or liquid all the way, or vapor all the way. That formula is
q = mass x specific heat in that phase x (Tfinal-Tinitial).
Then add each of the q values together to find the total heat required.
For ethanol at -135 up to -50.
So you will need q for solid from -135 to -114
Then melt it at -114
Then heat from -114 to -50.
Add the three.

Answer 2

6.91

Answer 3

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