A 5.000 g of Compound X with molecular formula C3H4 are burned in a constant-pressure calorimeter containing 15.00 kg of water at 25 °C. The temperature of the water is observed to rise by 3.688 °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.

THE STANDARD HEAT OF FORMATION FOR C3H8 IS 9.59 KJ/MOL.

Explanation:

Mass = 5 g of C3H4

Mass of water = 15 kg

Initial temperature of water = 25 C = 25 + 273 K = 298 K

Final temperature of water = 3.688 C = 3.688 + 273 K = 276.688 K

We may make the assumptions that:

1. the specific heat of water = 4.2 J/Kg K

2. total mass of the reaction mixture = 15 kg of water + 5 g of C3H8

= 15.005 Kg

Temperature change = 298 - 276.688 = 21.312 K

heat change for the reaction

Heat = mass * specific heat * change in temperture

Heat = 15.005 * 4.2 * 21.312

Heat = 1343.10 J

EQUATION

C3H8 + 5O2 -> 3CO2 + 4H2O + heat

Number of mole = mass / molar mass

Molar mass of HCl = 36.5 g/mol

Number of mole = 5 g/ 36.5 g/mol

Number of mole = 0.14 moles

5 g of C3H8 produces 1343.10 J of heat

0.14 mole of C3H8 produces 1343.10 J

1 mole of C3H8 will produce 1343.10 / 0.14 J of heat

= 9593.57 J

= 9.59 kJ of heat.

The standard heat of formation for C3H8 is 9.59 kJ/mol.