Question

1)  I have 50.0 g of ethanol (C2H5OH) at 100 K. I want gaseous ethanol at 373 K. How much energy do I need to add? Please show steps!

2) Consider the following reaction for the combustion of natural gas (CH4): CH4(g) + 2 O2(g) → CO2+ 2 H2O ∆Hrxn= - 882 kJ/mol

If I use this reaction as the source of heat in Question#1, how much methane would I need to burn to get my ethanol to 373 K?

Answer 1

1) The necessary heat in each stage is calculated:

i) Heating of solid:

q = m * cp * ΔT = 50 g * 2.44 J / g * K * (159 - 100) K = 7198 J

ii) Fusion of solid:

q = ΔHf * m = 109 J / g * 50 g = 5450 J

iii) Heating of the liquid:

q = 50 * 2.44 * (352 - 159) = 23546 J

iv) Evaporation of the liquid:

q = ΔHv * m = 841 J / g * 50 g = 42050 J

v) Steam heating:

q = 50 * 2.44 * (373 - 352) = 2562 J

The total heat required:

Total q = 80806 J = 80.81 kJ

2) The required methane moles are calculated:

n = q total / ΔH = 80.81 kJ / 882 kJ / mol = 0.09 mol

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