Given the following data: C s + 2 F 2 g → CF 4 g ; ∆ H 1 = - 680 kJ mol - 1 , F 2 g → 2 F g ; ∆ H 2 = + 158 kJ mol - 1 and C s → C g ; ∆ H 3 = + 715 kJ mol - 1 . Calculate te average bond enthalpy (in kJ mol - 1 ) for the C - F bond.

Consider the given data, C s + 2 F 2 g → CF 4 g ; ∆ H 1 = - 680 kJ mol - 1 -------(i) F 2 g → 2 F g ; ∆ H 2 = + 158 kJ mol - 1 -------(ii) C s → C g ; ∆ H 3 = + 715 kJ mol - 1 --------(iii) On multiplying equation (ii) by 2 , and reversing, we get, 4 F g → 2 F 2 g ; ∆ H 2 = - 2 × 158 kJ mol - 1 --------(iv) C g → C s ; ∆ H 3 = - 715 kJ mol - 1 ----------(v) (On reversing the equation (iii)) Then, after adding equations (i), (iv) and (v), we get the required equation, C g + 4 F g → CF 4 g ; ∆ H = - 680 + - 2 × 158 + - 715 = - 1711 kJ mol - 1 Therefore, average bond enthalpy of C - F bond = - 1711 4 = - 427 . 75 = 428 kJ mol - 1 .

Methanol is made in large quantities as it is used in the production of polymers and in fuels. The enthalpy of combustion of methanol can be determined theoretically or experimentally CH 3 OH l + 1 1 2 O 2 g → CO 2 g + 2 H 2 O g . Using the data from the given table, and determine the theoretical enthalpy of combustion of methanol. Bond C - H C - O O = O C = O O - H Average bond enthalpy ( kJ mol - 1 ) 412 358 496 743 463

Consider, the combustion reaction of methanol, CH 3 OH l + 1 1 2 O 2 g → CO 2 g + 2 H 2 O g . The amount of energy required to break bonds of reactants: 3 × BE C - H + 1 × BE C - O + 1 × BE O - H + 3 2 × BE O = O = 3 × 412 + 1 × 358 + 1 × 463 + 1 . 5 × 496 = 2801 kJ mol - 1 7580 kJ The amount of energy released during bond formation: 2 × BE C = O + 2 × 2 × BE O - H = 2 × 743 + 4 × 463 = 3338 kJ mol - 1 The enthalpy change of the reaction, ∆ H = ∑ (Bond Enthalpies of bonds broken) - ∑ (Bond Enthalpies of bonds formed) Therefore, ∆ H = 2801 - 3338 = - 537 kJ mol - 1

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure. The data shown in table were collected. Initial mass of burner and methanol / g 80 . 557 Final mass of burner and methanol / g 80 . 034 Mass of water in test tube / g 20 . 000 Initial temperature of water / ° C 21 . 5 Final temperature of water ° C 26 . 4 Calculate the amount, in mol , of methanol burnt.

Mass of methanol burnt = Initial mass of burner and methanol - Final mass of burner and methanol = 80 . 557 - 80 . 034 = 0 . 523 g The amount of methanol burnt in mol = Mass of methanol burnt Molecular mass of methanol g mol - 1 = 0 . 523 32 = 0 . 0163 mol .

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure. The data shown in table were collected. Initial mass of burner and methanol / g 80 . 557 Final mass of burner and methanol / g 80 . 034 Mass of water in test tube / g 20 . 000 Initial temperature of water / ° C 21 . 5 Final temperature of water ° C 26 . 4 Calculate the heat absorbed, kJ , by the water.

Initial temperature of water = 21 . 5 ° C and final temperature of water = 26 . 4 ° C . The increase in temperature, ∆ T = 26 . 4 - 21 . 5 = 4 . 9 ° C The heat absorbed by the water, q = m c ∆ T = 20 . 000 × 4 . 18 × 4 . 9 × 10 - 3 = 409 . 64 × 10 - 3 kJ .

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure. The data shown in table were collected. Initial mass of burner and methanol / g 80 . 557 Final mass of burner and methanol / g 80 . 034 Mass of water in test tube / g 20 . 000 Initial temperature of water / ° C 21 . 5 Final temperature of water ° C 26 . 4 Determine the enthalpy change, in kJ mol - 1 , for the combustion of one mole of methanol.

From the given data, the number of moles of methanol burnt = 0 . 0163 mol The heat absorbed during the combustion reaction, q = 0 . 41 kJ Therefore, the enthalpy change for the combustion of one mole of methanol, ∆ H c ° = - 0 . 41 0 . 0163 = - 25 . 153 kJ mol - 1 .

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure. The data shown in table were collected. Initial mass of burner and methanol / g 80 . 557 Final mass of burner and methanol / g 80 . 034 Mass of water in test tube / g 20 . 000 Initial temperature of water / ° C 21 . 5 Final temperature of water ° C 26 . 4 The data booklet value for the enthalpy of combustion of methanol is - 726 kJ mol - 1 . Suggest why this value differs from the values calculated experimentally.

Consider, the combustion reaction of methanol, CH 3 OH l + 1 1 2 O 2 g → CO 2 g + 2 H 2 O g The value of enthalpy of combustion of methanol determined by the given experimental data is found to be - 25 . 153 kJ mol - 1 , and the data booklet value for the enthalpy of combustion of methanol is - 726 kJ mol - 1 . Therefore, there is a difference in the values calculated from experimental data and the value of the data booklet. This is due to the fact that, during the reaction, not all heat produced transferred to water, heat lost to surroundings/environment. There may be also incomplete combustion of methanol, and the water forms as H 2 O l instead of H 2 O g as given in the thermochemical equation.

Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions

Author:Sergey Bylikin, Gary Horner & Brian Murphy

Sergey Bylikin Chemistry Solutions for Exercise - Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions

Attempt the practice questions on Chapter 5: Energetics and Thermochemistry, Exercise 6: Questions with hints and solutions to strengthen your understanding. Oxford IB Diploma Programme Chemistry Course Companion solutions are prepared by Experienced Embibe Experts.

Questions from Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions with Hints & Solutions

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 12

But- $1$ -ene gas burns in oxygen to produce carbon dioxide and water vapour according to the following equation:

$C_{4} H_{8} + 6 O_{2} \overset{}{\to} 4 {CO}_{2} + 4 H_{2} O$

The value of $∆ H^{\circ}$ for the combustion of But- $1$ -ene is calculated using the given data table, and is found to be $- 2068 kJ$ . State and explain whether the given reaction is endothermic or exothermic?

Bond	$C - C$	$C = C$	$C - H$	$O = O$	$C = O$	$O - H$
Average bond enthalpy ( $kJ {mol}^{- 1}$ )	$348$	$612$	$412$	$496$	$743$	$463$

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 13

Given the following data:

$C (s) + 2 F_{2} (g) \overset{}{\to} {CF}_{4} (g); ∆ H_{1} = - 680 kJ {mol}^{- 1}$ , $F_{2} (g) \overset{}{\to} 2 F (g); ∆ H_{2} = + 158 kJ {mol}^{- 1}$ and $C (s) \overset{}{\to} C (g); ∆ H_{3} = + 715 kJ {mol}^{- 1}$ . Calculate te average bond enthalpy (in $kJ {mol}^{- 1}$ ) for the $C - F$ bond.

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

Methanol is made in large quantities as it is used in the production of polymers and in fuels. The enthalpy of combustion of methanol can be determined theoretically or experimentally ${CH}_{3} OH (l) + 1 \frac{1}{2} O_{2} (g) \overset{}{\to} {CO}_{2} (g) + 2 H_{2} O (g)$ .

Using the data from the given table, and determine the theoretical enthalpy of combustion of methanol.

Bond	$C - H$	$C - O$		$O = O$	$C = O$	$O - H$
Average bond enthalpy ( $kJ {mol}^{- 1}$ )	$412$	$358$		$496$	$743$	$463$

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Diploma

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure.

Question Image

The data shown in table were collected.

Initial mass of burner and methanol / $g$	$80.557$
Final mass of burner and methanol / $g$	$80.034$
Mass of water in test tube / $g$	$20.000$
Initial temperature of water / $° C$	$21.5$
Final temperature of water $° C$	$26.4$

Calculate the amount, in

mol

, of methanol burnt.

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

Question Image

The data shown in table were collected.

Initial mass of burner and methanol / $g$	$80.557$
Final mass of burner and methanol / $g$	$80.034$
Mass of water in test tube / $g$	$20.000$
Initial temperature of water / $° C$	$21.5$
Final temperature of water $° C$	$26.4$

Calculate the heat absorbed,

kJ

, by the water.

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Diploma

IMPORTANT

Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

Question Image

The data shown in table were collected.

Initial mass of burner and methanol / $g$	$80.557$
Final mass of burner and methanol / $g$	$80.034$
Mass of water in test tube / $g$	$20.000$
Initial temperature of water / $° C$	$21.5$
Final temperature of water $° C$	$26.4$

Determine the enthalpy change, in $kJ {mol}^{- 1}$ , for the combustion of one mole of methanol.

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Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

Using the data from the given table, the value of enthalpy of combustion of methanol is found to be $- 537 kJ {mol}^{- 1}$ .

Bond	$C - H$	$C - O$		$O = O$	$C = O$	$O - H$
Average bond enthalpy ( $kJ {mol}^{- 1}$ )	$412$	$358$		$496$	$743$	$463$

The data booklet value for the enthalpy of combustion of methanol is $- 726 kJ {mol}^{- 1}$ . Suggest why this value differs from the values calculated theoretically.

EASY

Diploma

IMPORTANT

Oxford IB Diploma Programme Chemistry Course Companion>Chapter 5 - Energetics and Thermochemistry>Questions>Q 14

Question Image

The data shown in table were collected.

Initial mass of burner and methanol / $g$	$80.557$
Final mass of burner and methanol / $g$	$80.034$
Mass of water in test tube / $g$	$20.000$
Initial temperature of water / $° C$	$21.5$
Final temperature of water $° C$	$26.4$

The data booklet value for the enthalpy of combustion of methanol is $- 726 kJ {mol}^{- 1}$ . Suggest why this value differs from the values calculated experimentally.

Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions

Sergey Bylikin Chemistry Solutions for Exercise - Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions

Questions from Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Energetics and Thermochemistry, Exercise 6: Questions with Hints & Solutions

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