Calculate the standard enthalpy?

Question

Calculate the standard enthalpy change for the following reaction, assuming water (H2O) is produced in the gaseous state:
CH3OH (l) + 1.5 O2 (g) → CO2 (g) + 2 H2O (g)
Additionally, please calculate the heat produced by the combustion of methanol per liter. Note that methanol has a density of 0.791 g/mL. Furthermore, calculate the mass of carbon dioxide (CO2) produced per kilojoule (kJ) of heat emitted during this reaction.

Anonymous · Accepted Answer

Calculate the standard enthalpy change for the reaction, assuming H2O (g) as a product.

***Just use the standard heat of reactions for each substance in the balanced equation (found in appendix C if you're using Chemistry The Natural Science), and use Hess's Law (deltaH=sum of (number of moles)(deltaH of products) - sum of (number of moles)(deltaH of reactants).

[-393.5 + 2(-241.82)] - [-238.6 + (3/2)(0)]

= -638.54 (four sig figs = -638.5)

Calculate the heat produced by combustion per liter of methanol. Methanol has a density of 0.791 g/mL.

***Follow the units to find your answer... you want to go from g/mL to kJ/L

.791 g/mL (10^3mL/1L)(1mol methanol/32.04g)(-638.5kJ/1mol methanol)=1.58x10^4

Calculate the mass of CO2 produced per kJ of heat emitted.

***Again just use what you have and follow your units. 1 mol of CO2 is used for every 1 mol of methanol. The molar mass of CO2 is 40.010g. You divide that by the enthalpy of reaction (in kJ). This way you will end up with g/kJ.

40.010g/638.5kJ(negative sign isn't used here) = 6.892x10^-2

Anonymous

Calculate the standard enthalpy?

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