Extra ΔH QUESTIONS for Advanced Level Chemistry Enthalpy Calculation Revision Questions A selection of practice exam calculation questions is presented dealing with enthalpy of formation, enthalpy of combustion, standard enthalpy measurements and data and problem solving using Hess's Law including enthalpy of reaction via bond enthalpy calculations. Enthalpy questions are set out on this page and the logical deductions of the answers are set out on another page. I hope this will help you to be more proficient in solving enthalpy data problem calculations. EMAIL Recently, some corrections and re-editing have been applied to questions 1, 3, 4 and 8 concerning bond enthalpy (bond energy) calculations and apologies for still not typing up the original scribbled out answers, though the additional calculations have been typed up neatly on the answer page! Associated LINKS 1. Thermodynamics Part 1: Thermochemistry - Calorimetry experiments - Enthalpies of reaction, formation, combustion and bond dissociation are explained with exemplar calculations 2. ANSWERS to the ΔH enthalpy Q's below 3. GCSE/IGCSE/O Level notes Energy Changes, exothermic/endothermic reactions See also fully worked out examples from calorimeter data and using Hess's Law cycles to solve problems (a) Define the standard enthalpy of (i) combustion, Δ^{H}_{θc}, and (ii) formation, ΔH^{θ}_{f} (b) Given the following standard enthalpies of combustion, ΔH^{θ}_{c} (298K, 1 atm)
Note: the first two enthalpies correspond to the standard enthalpy of formation of carbon dioxide and water respectively
(c) Given the following bond enthalpies (bond energies) in kJmol^{-1}
ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 2 Given the following standard enthalpies of combustion ΔH^{θ}_{c} (298K, 1 atm)
Calculate the standard enthalpy of formation of octane, ΔH^{θ}_{f}(C_{8}H_{18}(l)) ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 3 (a) Given the following standard enthalpies of combustion ΔH^{θ}_{c}(298K, 1 atm)
and the standard enthalpy of formation of liquid cyclohexane, ΔH^{θ}_{f}(C_{6}H_{12}(l)) = -156 kJ mol^{-1}
(b) Using the appropriate bond energies from Q1c, calculate the theoretical enthalpy of combustion of cyclohexane, assuming ALL reactants and products are gases.
(c) If the enthalpy of vapourisation of water is +40.7 kJmol^{-1} and the enthalpy of vapourisation of cyclohexane is +30.0 kJmol^{-1}, from your answer to (b), recalculate the enthalpy of combustion of cyclohexane.
(d) Compare and comment on your answers to (a), (b) and (c) and, where appropriate, quote percentage errors. ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 4 (a) Given the following standard enthalpies of combustion ΔH^{θ}_{c }(298K, 1 atm)
and the enthalpy of formation of ethanoic acid, ΔH^{θ}_{f}(CH_{3}COOH(l)) = -487 kJ mol^{-1} Calculate the standard enthalpy of combustion of ethanoic acid, ΔH^{θ}_{c}(CH_{3}COOH(l)) (b) Using the bond enthalpies listed in Q1(c), and assuming all reactants and products are gases, calculate the enthalpy of combustion of ethanoic acid, noting that the bond enthalpy for C=O is +743 kJmol^{-1} when it is NOT in the carbon dioxide molecule. (c) If the enthalpy of vaporisation of ethanoic acid is 51.6 kJmol^{-1} and the enthalpy of vaporisation of water is 40.7 kJmol^{-1}, use your answer from (b) to calculate the enthalpy of combustion of ethanoic acid under standard conditions, ie a corrected value to take into account the standard states of reactants and products at 298K/1atm. (d) Compare and comment on the three values of ΔH_{comb}(ethanoic acid) calculated in parts (a), (b) and (c). ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 5 Given the following standard enthalpies of formation ΔH^{θ}_{f}(298K, 1 atm)
Calculate the standard enthalpy change for the reaction, ΔH^{θ}_{r}
ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 6 Given the following standard enthalpies of formation, ΔH^{θ}_{f}, in kJmol^{-1 }(298K, 1 atm)
Calculate the standard enthalpy change for the reaction, ΔH^{θ}_{r}
ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 7 (a) Define the term 'average bond enthalpy'. (b) Given the following standard enthalpies of formation, ΔH^{θ}_{f} in kJmol^{-1} (298K, 1 atm)
Calculate the standard enthalpy change for the reaction, ΔH^{θ}_{r}
(c) Given the following average bond energies in kJmol^{-1} bond ΔH_{BE}: C-H 412 ; Cl-Cl 242 ; C-Cl 338 ; H-Cl 431 Calculate the enthalpy change for the same reaction as in (b) (d) Explain which of the calculations in (b) or (c) will be the most accurate and why? ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 8 (a) Given the following standard enthalpies of formation, ΔH^{θ}_{f} in kJ mol^{-1} at 298K, 1 atm C_{2}H_{6}(g) -84.7 ; C_{2}H_{5}I(l) -39.1 ; HI(g) +25.9 Without using a Hess's Law Cycle, calculate the standard enthalpy change, ΔH^{θ}_{r} for the reaction: C_{2}H_{6}(g) + I_{2}(s) ====> C_{2}H_{5}I(l) + HI(g) (b) Given the following average bond energies in kJ mol^{-1} bond ΔH_{BE}: C-H 412 ; C-I 228 ; H-I 299, and the enthalpy of vapourisation of iodoethane is 32.0 kJmol^{-1},
(c) How do your answers to (a) and (b) compare? ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes
Question 9 Given the bond enthalpies (ΔH_{BE}) in kJ mol^{-1}: C-H 412, C-C 348 and H-H 436 (∆H_{atom} = 218 kJ mol^{-1}). Calculate the enthalpy of formation of propane if the enthalpy of atomisation of carbon (graphite) is 715kJ mol^{-1}. ANSWERS to the ΔH enthalpy Q's * Thermochemistry and Enthalpy Notes See also fully worked out examples from calorimeter data and using Hess's Law cycles to solve problems using enthalpy of combustion in calculation questions, using enthalpy of formation in calculation questions how to do A level enthalpy calculations for AQA AS chemistry, how to do A level enthalpy calculations for Edexcel A level AS chemistry, how to do A level enthalpy calculations for A level OCR AS chemistry A, how to do A level enthalpy calculations for OCR Salters AS chemistry B, how to do A level enthalpy calculations for AQA A level chemistry, how to do A level enthalpy calculations for A level Edexcel A level chemistry, how to do A level enthalpy calculations for OCR A level chemistry A, how to do A level enthalpy calculations for A level OCR Salters A level chemistry B how to do A level enthalpy calculations for US Honours grade 11 grade 12 how to do A level enthalpy calculations for pre-university chemistry courses pre-university A level revision notes for how to do A level enthalpy calculations A level guide notes on how to do A level enthalpy calculations for schools colleges academies science course tutors images pictures diagrams for how to do A level enthalpy calculations A level chemistry revision notes on how to do A level enthalpy calculations for revising module topics notes to help on understanding of how to do A level enthalpy calculations university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on how to do A level enthalpy calculations Edexcel A level chemistry notes on how to do A level enthalpy calculations for OCR A level chemistry notes WJEC A level chemistry notes on how to do A level enthalpy calculations CCEA/CEA A level chemistry notes on how to do A level enthalpy calculations for university entrance examinations how do you do bond enthalpy calculation questions? how do you do enthalpy calculations? how do you do calculations using enthalpies of formation and enthalpies of combustion? practice enthalpy questions for advanced A level chemistry, how do you calculate an unknown enthalpy change using Hess's law and known enthalpy values? practice bond enthalpy calculation questions
See also fully worked out examples from calorimeter data and using Hess's Law cycles to solve problems |
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