Question

4.000 g of Compound X with molecular formula C H are burned in a constant-pressure calorimeter containing 40.00 kg of water at 25 °C. The temperature of the water is observed to rise by 1.065 °C. (You may assume all the heat released by the reaction is absorbed by the water, and none by the calorimeter itself.) Calculate the standard heat of formation of Compound X at 25 °C.

Answer 1

Explanation:

2407 kJ/mol

Explanation:

Given:

Mass of water = 40.00 kg

\Delta TΔT = 1.065 °C

Net Heat transfer during heating:

Q=m_{water}\times C_{water}\times \Delta TQ=m

water

×C

water

×ΔT

Specific heat of water = 4.187 kJ/kg°C

Q=40.00\times 4.187\times 1.065\ kJQ=40.00×4.187×1.065 kJ

Q = 178.3662 kJ

Heat gained by water is heat lost by the compound. Thus, heat lost = 178.3662 kJ

Also,

Mass = 4.000 g

Molar mass of C_4H_6=4\times 12+6\times 1\ g/mol=54\ g/molC

4

H

6

=4×12+6×1 g/mol=54 g/mol

The formula for the calculation of moles is shown below:

moles = \frac{Mass\ taken}{Molar\ mass}moles=

Molar mass

Mass taken

Thus,

Moles= \frac{4.000\ g}{54\ g/mol}Moles=

54 g/mol

4.000 g

Moles= 0.0741\ molMoles=0.0741 mol