Question

The molar heat of combustion of liquid ethyl alcohol is -1336.91 kcal/mole. If 300 mg of ethyl alcohol is burned in a calorimeter causes a rise in temperature of 2.225oC. What is the total heat capacity of the calorimeter?

Answer 1

Molar heat of combustion of liquid ethyl alcohol, Q = -1336.91 kcal/mol

Calorimeter gives temperature rise, ΔT = 2.225 C.

Mass of ethyl alcohol, m = 300 mg = 300*10^-3 gm = 0.3 gm

Ethyl alcohol(C2H5OH) molar mass M = 12*2 + 1*6 + 1*16 = 46 gm/mol

Moles of ethyl alcohol, n = m/M = 0.3 gm/(46gm/mol) = 6.52*10^-3 mole

As we know that for calorimeter,

Q = Qcal + Qwater

Q = Ccal*ΔT + Cw*ΔT

Q = (Ccal + Cw) *ΔT

Q = Ctotal*ΔT

Where Ccal - heat capacity for calorimeter .(cal/C)

Cw - heat capacity for water. (cal/C)

Ctotal = Ccal + Cw - total heat capacity for calorimeter.

Q(cal)  is the heat released or absorbed by calorimeter for any substance.

Here Q is liberated due to ethyl alcohol.

Q = - 1336.91 cal/mol * 6.52*10^-3 mol =- 8.716 cal

We use (-) sign only for showing heat liberated from the system.

Q = Ctotal*ΔT

8.716Cal= Ctotal*2.225 C

Ctotal = 8.716Cal/2.225 C

Ctotal = 3.917 cal/C

total Heat capacity for calorimeter, Ctotal = 3.917 cal/C.

ans : 3.917 cal/C