Question

The combustion of 0.450 g of benzi od (cm 3,220 /mol, HW - 172 17 g/mol in a borb calorimeter increased the temperature of the calorimeter by 1.621°C. The chamber was the emptied and recharged with glucose (MW-180.16 g/mol) and excess oxygen. Ignition of the glucose rested in a temperature increase of 3.600'C. How many grams of cose were combusted? for gcois 2.780 /mol My Notes

Answer 1

Mass of benzoic acid is 0.450 g. The molar mass of benzoic acid is 122.12 g/mol.

The number of moles of benzoic acid

0.450 g =0.003685 mol 122.12 g/mol

The enthalpy of combustion of benzoic acid is

A H comb = 3228 kJ/mol

The amount of heat released during combustion of benzoic acid

9 = AH comb X number of moles = 3228 kJ/mol x 0.003685 mol = 11.89 kJ

Temperature change

AT = 1.621

The calorimeter constant

C= 11.89 kJ AT 1.621 OC = 7.34 kJ/°C

For glucose,

The enthalpy of combustion of glucose is

A H comb = 2780 kJ/mol

Temperature change

AT = 3,600

The amount of heat released during combustion of glucose

... ... (1)

q= AH comb X number of moles = 2780 kJ/mol x number of moles

The amount of heat released during combustion of glucose

......(2)

q = C x ST = 7,34 kJC x 3.600 °C = 26.4 iJ

but (1) = (2)

2780 kJ/mol x number of moles = 26.4 kJ

number of moles = 0.0095 mol

The molar mass of glucose is 180.16 g/mol.

The mass of glucose combusted

= 0.0095 mol x 180.16 g/mol = 1.71 g