Name: Absolute Zero and Third Law of Thermodynamics
Uploaded: 2019-07-19
Duration: 20 min
Description: In this video, you will learn what absolute zero and the third law of thermodynamics is. You will also learn about the significance of the third law of therm...

Question

Compare the quantity of heat produced by the combustion of

1.0 g

glucose

(C_{6} H_{12} O_{6})

with that produced by

1.0 g

sucrose

(C_{12} H_{22} O_{11})

. Given that the standard heats of formation of

{CO}_{2}, H_{2} O

, glucose and sucrose are

- 393.5, - 285.9, - 1260 and - 2221 kJ {mol}^{- 1}

respectively.

Accepted Answer

Given,

$(i) C_{6} H_{12} O_{6} + 6 O_{2} (g) \overset{∆}{\to} 6 {CO}_{2} + 6 H_{2} O; {ΔH}_{1} = ?$

$- 393.5, - 285.9, - 1260 and - 2221 kJ {mol}^{- 1}$ .

Given heat of formation of ${CO}_{2} = - 393.5 kJ {mol}^{- 1}$ .

Given heat of formation of $H_{2} O = - 285.9 kJ {mol}^{- 1}$ .

Given heat of formation of $C_{6} H_{12} O_{6} = - 1260 kJ {mol}^{- 1}$ .

Given heat of formation of $C_{12} H_{22} O_{11} = - 2221 kJ {mol}^{- 1}$ .

Using $eq (1)$ ,

${ΔH}_{reaction} = {ΔH}_{product} - {ΔH}_{reactant}$ .

$= (6 {ΔH}_{{CO}_{2}} + 6 {ΔH}_{water}) - ({ΔH}_{glucose} + 6 {ΔH}_{O_{2}}) . = ((6 \times 393.5) + (6 \times (- 285.9))) - (- 1260 + (2 \times 0)) . = (- 2361 - 1715.4) + 1260 . = (- 4076.4) + (1260) = - 2816.4 kJ {mol}^{- 1} .$
Heat produced from $1 g$ of glucose $= - \frac{2816.4}{180} = - 15.64 kJ$ .

Using $eq (2)$ ,

${ΔH}_{reaction} = {ΔH}_{product} - {ΔH}_{reactant}$ .

$= (12 {ΔH}_{{CO}_{2}} + 11 {ΔH}_{water}) - ({ΔH}_{sucrose} + 6 {ΔH}_{O_{2}}) . = ((12 \times 393.5) + (11 \times (- 285.9))) - (- 2221 + (2 \times 0)) . = (- 4722 - 3144.9) + 2221 = (- 7866.9) + (2221) . = - 5645.9 kJ {mol}^{- 1} .$
Heat produced from $1 g$ of sucrose $= - \frac{5645.9}{342} = - 16.5 kJ$ .

Important Questions on Thermodynamics

Learn and Prepare for any exam you want !

Compare the quantity of heat produced by the combustion of 1.0 g glucose (C6H12O6) with that produced by 1.0 g sucrose (C12H22O11). Given that the standard heats of formation of CO2, H2O, glucose and sucrose are –393.5, –285.9, –1260 and –2221 kJ mol-1 respectively.

Important Questions on Thermodynamics

Learn and Prepare for any exam you want !