Question

A 5.000 g sample of methanol, CH3OH, was combusted in the presence of excess oxygen in a bomb calorimeter. The temperature of the water in the calorimeter increased from 24.000 °C to 29.765 °C. The heat capacity of the calorimeter was 2.657 kJ/°C. Calculate AH for the reaction below.

2CH₃OH + 30₂ → 2CO₂ + 4H₂O
a. -395 kJ
b. -197 kJ
c.-98.7 kJ
d.-30.6 kJ
e. -15.3 kJ

Answer 1

The heat of combustion for 1 mole of methanol is found to be -98.09 kJ. This was calculated by determining the heat absorbed by the calorimeter during combustion and then dividing by the number of moles of methanol combusted. So the closest option to the correct option is C.

Step-by-step explanation:

To calculate the enthalpy change (ΔH) for the combustion of methanol, we need to find out how much heat was absorbed by the water in the calorimeter and then relate it to the amount of methanol burned. The heat absorbed by the water can be found by multiplying the heat capacity of the calorimeter by the temperature change, which is:

q = C × ΔT

Where C is the heat capacity of the calorimeter and ΔT is the temperature change. Next, we calculate the heat absorbed using the given data:

q = 2.657 kJ/°C × (29.765 °C - 24.000 °C)

q = 2.657 kJ/°C × 5.765 °C

q = 15.303505 kJ

This is the heat absorbed by the calorimeter for the combustion of a 5.000 g sample of methanol. Since this reaction is exothermic, the released heat should be negative. The molar mass of methanol (CH3OH) is approximately 32.04 g/mol, so the sample represents 5.000 g / 32.04 g/mol = 0.156 mol methanol. To find the heat of combustion per mole of methanol, we divide the total heat released by the number of moles:

ΔH = -q / n

ΔH = -15.303505 kJ / 0.156 mol

ΔH = -98.09 kJ/mol

Therefore, the heat of combustion for 1 mole of methanol is -98.09 kJ, which corresponds to option c, -98.7 kJ, when rounded to three significant figures.

Answer 2

To calculate the enthalpy change (ΔH) for the combustion of methanol in a bomb calorimeter, multiply the heat capacity of the calorimeter by the temperature change in the water and apply the negative sign. Then, normalize this value to the amount of methanol used to find the ΔH per mole of methanol. So, the correct option is d.-30.6 kJ

Step-by-step explanation:

The student is asking how to calculate the enthalpy change (ΔH) for the combustion of methanol (CH₃OH) in a bomb calorimeter.

The data provided indicates that 5.000 g of methanol was combusted, resulting in a temperature increase of the water in the calorimeter from 24.000 °C to 29.765 °C.

The heat capacity of the calorimeter is given as 2.657 kJ/°C. The enthalpy change for the reaction can be determined using the formula:

ΔH = - (Heat capacity of the calorimeter x temperature change)

This method allows determining the heat of combustion on a per mole basis, considering that the molar mass of methanol is 32.04 g/mol.

The reaction equation given is the balanced chemical equation for the combustion of methanol:

2CH₃OH(l) + 3O₂(g) → 2CO₂(g) + 4H₂O(l)

So, the correct option is d.-30.6 kJ