Homework SourseWhen 1535 g of methanol CH3OH was burned in a constantvolume
When 1.535 g of methanol (CH3OH) was burned in a constant-volume bomb calorimeter, the water temperature rose from 20.27 degrees C to 26.87 degrees C. If the mass of water surrounding the calorimeter was exactly 1000 g and the heat capacity of the bomb calorimeter was 1.75kJ/degrees C, calculate the molar heat of combustion of methanol. The specific heat of water is 4.184J/g*degrees C.
Solution
Reasoning And Solution :
because this is an isolated system the heatgenerated from the combustion must be equal to the heat gained bythe water and calorimeter.First we calculate the heat changes forthe water and calorimeter .
From the equation q = mst
qwater =( 1000 g) (4.184 J / g 0C )(26.870C- 20.270C)
= 2.76*104 J
qbomb = (1.75*103J/0C)(26.870C- 20.270C)
= 1.15*104 J
qrxn =-(2.76*104 J+1.15*104 J)
= -3.91*104 J
The molar mass of Methanol(CH3OH) is 32.0420 g/mol .So the Heat of combustion of 1mole of Methanol is
molar heat of combustion = (-3.91*104 J) / (1.535 gCH3OH) *(32.0420 g )/(1mole CH3OH)
= -8.16*105 J /mol
= - 8.16*102 KJ /mol
