ThermochemistryHard

Question

Calculate the heat effect produced when a solution of 1 mole of ethanol in 5 moles of water is mixed with a solution of 2 moles of ethanol in 20 moles of water.

C2H5OH + 5H2O → C2H5OH (5H2O): ΔH = −1120 cal

C2H5OH + 10H2O → C2H5OH (10H2O): ΔH = −1760 cal

C2H5OH + (25/3)H2O → C2H5OH (25/3 H2O): ΔH = −1650 cal

Options

A.310 cal is absorbed.
B.310 cal is released.
C.4640 cal is absorbed.
D.4640 cal is released.

Solution

$3C_{2}H_{5}OH + 25H_{2}O \rightarrow 3C_{2}H_{5}OH\left( 25H_{2}O \right);$

$\Delta H_{\text{theo}} = ( - 1120) + 2( - 1760) = - 4640\text{ kcal}$

$\Delta H_{\text{theo}} = 3( - 1650) = - 4950\text{ cal}$

As experimentally, more heat is released means the mixing is exothermic by (4950 – 4640) = 310 cal.

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