Question

4.000 g of Compound X with molecular formula C4H6 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. Be sure your answer has a unit symbol, if necessary, and round it to the correct number of significant digits.

Answer 1

Answer:

2407 kJ/mol

Explanation:

Given:

Mass of water  = 40.00 kg

$\Delta T$  = 1.065 °C

Net Heat transfer during heating:

$Q=m_{water}\times C_{water}\times \Delta T$

Specific heat of water = 4.187 kJ/kg°C  

$Q=40.00\times 4.187\times 1.065\ kJ$

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 $C_4H_6=4\times 12+6\times 1\ g/mol=54\ g/mol$

The formula for the calculation of moles is shown below:

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

Thus,

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

$Moles= 0.0741\ mol$

Standard heat of formation = 178.3662 kJ / 0.0741 mol=2407 kJ/mol (In correct significant digits)