Answer:
The heat of combustion per moles of caffeine is 4220 kJ/mol
Explanation:
Step 1: Data given
⇒ When benzoic acid sample of 0.245 grams is burned the temperature rise is 1.643 °C
⇒ When 0.260 gram of caffeine is burned, the temperature rise is 1.436 °C
⇒ Heat of combustion of benzoic acid = 26.38 kJ/g
<u>Step 2:</u> Calculate the heat released: for combustion of benzoic acid
0.245 g benzoic acid * 26.38 kJ/g = 6.4631 kJ
<u>Step 3</u>: Calculate the heat capacity of the calorimeter:
c = Q/ΔT
Q = 6.4631 kJ / 1.643°C = 3.934 kJ/ °C
<u>Step 4:</u> Calculate moles of a 0.260 g sample of caffeine:
Moles caffeine = Mass caffeine / Molar mass caffeine
0.260 grams/ 194.19 g/mol = 0.0013389 moles
Step 5: Calculate heat released: for combustion of caffeine
Q = c * ΔT
Q = 3.934 kJ/°C * 1.436 °C = 5.65 kJ
Step 6: Calculate the heat of combustion per mole of caffeine
5.65 kJ / 0.0013389 moles = 4219.9 kJ/mol ≈ 4220 kJ/mol
The heat of combustion per moles of caffeine is 4220 kJ/mol
