Respuesta :
Answer : The heat of combustion per mole of caffeine at constant volume is 76197.18 kJ/mole
Explanation :
First we have to calculate the specific heat calorimeter.
Formula used :
[tex]Q=m\times c\times \Delta T[/tex]
where,
Q = heat of combustion of benzoic acid = 26.38 kJ/g = 26380 J/g
m = mass of benzoic acid = 0.235 g
c = specific heat of calorimeter = ?
[tex]\Delta T[/tex] = change in temperature = [tex]1.643^oC[/tex]
Now put all the given value in the above formula, we get:
[tex]26380J/g=0.235g\times c\times 1.643^oC[/tex]
[tex]c=68323.38J/^oC[/tex]
Thus, the specific heat of calorimeter is [tex]68323.38J/^oC[/tex]
Now we have to calculate the heat of combustion of caffeine.
Formula used :
[tex]Q=c\times \Delta T[/tex]
where,
Q = heat of combustion of caffeine = ?
c = specific heat of calorimeter = [tex]68323.38J/^oC[/tex]
[tex]\Delta T[/tex] = change in temperature = [tex]1.584^oC[/tex]
Now put all the given value in the above formula, we get:
[tex]Q=68323.38J/^oC\times 1.584^oC[/tex]
[tex]Q=108224.23J=108.2kJ[/tex]
Now we have to calculate the moles of caffeine.
[tex]\text{Moles of caffeine}=\frac{\text{Mass of caffeine}}{\text{Molar mass of caffeine}}[/tex]
Mass of caffeine = 0.275 g
Molar mass of caffeine = 194.19 g/mole
[tex]\text{Moles of caffeine}=\frac{0.275g}{194.19g/mole}=0.00142mol[/tex]
Now we have to calculate the heat of combustion per mole of caffeine at constant volume.
[tex]\text{Heat of combustion per mole of caffeine}=\frac{108.2kJ}{0.00142mol}=76197.18kJ/mole[/tex]
Therefore, the heat of combustion per mole of caffeine at constant volume is 76197.18 kJ/mole
