Consider the following reaction: 2 CH3OH1g2 ¡ 2 CH41g2 + O21g2 H = +252.8 kJ (a)
ID: 517949 • Letter: C
Question
Consider the following reaction:
2 CH3OH1g2 ¡ 2 CH41g2 + O21g2 H = +252.8 kJ
(a) Is this reaction exothermic or endothermic? (b) Calculate
the amount of heat transferred when 24.0 g of CH3OH1g2 is
decomposed by this reaction at constant pressure. (c) For a
given sample of CH3OH, the enthalpy change during the
reaction is 82.1 kJ. How many grams of methane gas are
produced? (d) How many kilojoules of heat are released
when 38.5 g of CH41g2 reacts completely with O21g2 to form
CH3OH1g2 at constant pressure?
Explanation / Answer
2 CH3OH ---------------> 2 CH4 + O2 H = +252.8 kJ
a)
This reaction is endothermic . because H is positive
b)
mass of CH3OH = 24.0 g
moles of CH3OH = 24 / 32.04 = 0.749 mol
H = +252.8
H = - Q / n
252.8 = Q / 0.749
amount of heat transferred = 189.4 kJ
c)
2 CH3OH ---------------> 2 CH4 + O2 H = +252.8 kJ
32 g CH4 -------------> 252.8 kJ
?? -----------------> 82.1 kJ
mass of methane = 10.39 g
d)
32 g CH4 -------------> 252.8 kJ
38.5 g CH4 ---------------> ??
heat = 304.2 kJ