Question

A chemical compound has a molecular weight of 89.05 g/mole. 1.400 grams of this compound underwent complete combustion under constant pressure conditions in a special calorimeter. This calorimeter had a heat capacity of 2980 J °C.1 (Note that the calorimeter was made of a metal shell, a water "substitute" - a special oil, and a thermocouple). The temperature went up by 11.95 degrees. Calculate the molar heat of combustion of the compound .

1. How much heat was given off by the combustion reaction, based on the temperature rise of the calorimeter?
2. How many moles of compound were used up to provide this heat?
3. How much heat would one mole of compound provide?
4. Is the combustion of this compound exothermic or endothermic?
5. Would the molar enthalpy of combustion for this compound be a negative quantity or a positive quantity?

Answer 1

The molar heat of combustion for the compound is calculated by finding the total heat released, the number of moles of the compound, and then dividing the heat by the moles. The reaction is exothermic, and the molar enthalpy of combustion would be negative.

Step-by-step explanation:

The student is asking how to calculate the molar heat of combustion for a compound given data from a combustion reaction in a calorimeter. Here are the steps to find the answers:

1. To find the total heat released (q), multiply the heat capacity of the calorimeter by the temperature increase: q = 2980 J/°C * 11.95 °C = 35621 J.
2. The number of moles of the compound is found by dividing the mass used (1.400 g) by the molecular weight (89.05 g/mol): moles = 1.400 g / 89.05 g/mol = 0.01572 mol.
3. To calculate the heat per mole, divide the total heat by the number of moles: 35621 J / 0.01572 mol = 2266059.54 J/mol or 2266.06 kJ/mol. This value is the molar heat of combustion.
4. Since the temperature increased, the combustion is exothermic.
5. The molar enthalpy of combustion will be a negative quantity, reflecting the release of energy.