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Vesnalui [34]
3 years ago
10

When a 0.245-g sample of benzoic acid is combusted in a bomb calorimeter, the temperature rises 1.643 ∘C . When a 0.260-g sample

of caffeine, C8H10O2N4, is burned, the temperature rises 1.436 ∘C . Using the value 26.38 kJ/g for the heat of combustion of benzoic acid, calculate the heat of combustion per mole of caffeine at constant volume.
Chemistry
1 answer:
sveticcg [70]3 years ago
4 0

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

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