2. Consider the following reaction: 2CH3OH(g) → 2 CH4(g) + O2(g) H=+252.8 kJ
a. this reaction is endothermic because the sign of enthalpy given is positive
b. Calculate the amount of heat transferred when 24.0 g of CH3OH(g) is decomposed by this reaction at constant pressure.
moles of CH3OH= 24.0g/32.04 g/mol=0.749moles
2moles of CH3OH absorbs +252.8kJ
=0.749moles x (+252.8kJ/2moles)=94.7kJ
c. For a given sample of CH3OH, the enthalpy change during the reaction is 82.1 kJ. How many grams of methane, CH4, are produced?
2 moles of CH3OH absorbs +252.8kJ
=82.1kJ x (2moles/+252.8kJ)=0.6495moles
molar mass of CH3OH= 32.04g/mol
mass=0.6495moles x 0.6495moles=20.8g
d. How many kilojoules of heat are released when 38.5 g of CH4 (g) reacts completely with O2 (g) to form CH3OH( g) at constant pressure?
moles of CH3OH=38.5g/32.04g/mol=1.2016moles
2 moles of CH3OH absorbs +252.8kJ
thus
=1.2016moles x (252.8kJ/2moles)=151.9kJ