Sections A. Hess s Law Grade 12. Energetics. Instructions: Please complete questions: 1-9 for homework

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1 Hess s Law Grade 2 Energetics Instructions: Please complete questions: - 9 for homework Sections A. The H Ө values for the formation of two oxides of nitrogen are given below. 2 N 2 (g) + O 2 (g) NO 2 (g) H Ө = 57 kj mol N 2 (g) + 2O 2 (g) N 2 O 4 (g) H Ө = +9 kj mol Use these values to calculate H Ө for the following reaction (in kj): A. 05 B. 48 C. +66 D NO 2 (g) N 2 O 4 (g) 2. The standard enthalpy change of formation values of two oxides of phosphorus are: P 4 (s) + 3O 2 (g) P 4 O 6 (s) H Ө f= 600 kj mol P 4 (s) + 5O 2 (g) P 4 O 0 (s) H Ө f= 3000 kj mol What is the enthalpy change, in kj mol, for the reaction below? P 4 O 6 (s) + 2O 2 (g) P 4 O 0 (s) A B C. 400 D. 4600

2 3. The following equations show the oxidation of carbon and carbon monoxide to carbon dioxide. C(s) +O 2 (g) CO 2 (g) H Ө = x kj mol CO(g) + 2 O 2 (g) CO 2 (g) H Ө = y kj mol l What is the enthalpy change, in kj mol, for the oxidation of carbon to carbon monoxide? A. x + y B. x y C. y x D. x y C(s) + 2 O 2 (g) CO(g) 4. The equations and enthalpy changes for two reactions used in the manufacture of sulfuric acid are: S(s) O 2 (g) SO 2 (g) 2SO 2 (g) + O 2 (g) 2SO 3 (g) H Ө = 300 kj H Ө = 200 kj What is the enthalpy change, in kj, for the reaction below? 2S(s) + 3O 2 (g) 2SO 3 (g) A. 00 B. 400 C. 500 D Using the equations below: C(s) + O 2 (g) CO 2 (g) Mn(s) + O 2 (g) MnO 2 (s) H = 390 kj H = 520 kj what is H (in kj) for the following reaction? MnO 2 (s) + C(s) Mn(s) + CO 2 (g) A. 90 B. 30 C. 30 D. 90 2

3 6. Using the equations below Cu(s) + 2 O 2 (g) CuO(s) H ο = 56 kj 2Cu(s) + 2 O 2 (g) Cu 2 O(s) H ο = 70 kj what is the value of H ο (in kj) for the following reaction? 2CuO(s) Cu 2 O(s) + 2 O 2 (g) A. 42 B. 5 C. 5 D Consider the following equations. Mg(s) + 2 O 2 (g) MgO(s) H 2 (g) + 2 O 2 (g) H 2 O(g) H ο = 602 kj H ο = 242 kj What is the H value (in kj) for the following reaction? MgO(s) + H 2 (g) Mg(s) + H 2 O(g) A. 844 B. 360 C D Separate solutions of HCl(aq) and H 2 SO 4 (aq) of the same concentration and same volume were completely neutralized by NaOH(aq). X kj and Y kj of heat were evolved respectively. Which statement is correct? A. X = Y B. Y = 2X C. X = 2Y D. Y = 3X 3

4 9. Section B. Calculate the enthalpy change, H 4 for the reaction C + 2H O 2 CH 3 OH H 4 using Hess s Law and the following information. CH 3 OH + O 2 2 CO 2 + 2H 2 O H = 676 kj mol C + O 2 CO 2 H 2 = 394 kj mol H O 2 H 2 O H 3 = 242 kj mol (Total 4 marks) 4

5 2. Calculate the enthalpy change, H 4 for the reaction C + 2H O 2 CH 3 OH H 4 using Hess s Law, and the following information. CH 3 OH + O 2 2 CO 2 + 2H 2 O H = 676 kj mol C + O 2 CO 2 H 2 = 394 kj mol H O 2 H 2 O H 3 = 242 kj mol (Total 4 marks) 3. Two reactions occurring in the manufacture of sulfuric acid are shown below: reaction I S(s) +O 2 (g) SO 2 (g) H Ө = 297 kj reaction II SO 2 (g) + 2 O 2 (g) SO 3 (g) H Ө = 92 kj (i) (ii) (iii) State the name of the term H Ө. State, with a reason, whether reaction I would be accompanied by a decrease or increase in temperature. At room temperature sulfur trioxide, SO 3, is a solid. Deduce, with a reason, whether the H Ө value would be more negative or less negative if SO 3 (s) instead of SO 3 (g) were formed in reaction II. Deduce the H Ө value of this reaction: (3) (2) S(s) + O 2 2 (g) SO 3 (g) (Total 6 marks) 5

6 4. The data below is from an experiment used to measure the enthalpy change for the combustion of mole of sucrose (common table sugar), C 2 H 22 O (s). The time-temperature data was taken from a data-logging software programme. Mass of sample of sucrose, m = g Heat capacity of the system, C system = 0.4 kj K (a) Calculate ΔT, for the water, surrounding the chamber in the calorimeter. (b) Determine the amount, in moles, of sucrose. 6

7 (c) (i) Calculate the enthalpy change for the combustion of mole of sucrose (ii) Using Table 2 of the Data Booklet, calculate the percentage experimental error based on the data used in this experiment (d) A hypothesis is suggested that TNT, 2-methyl-,3,5-trinitrobenzene, is a powerful explosive because it has: a large enthalpy of combustion a high reaction rate a large volume of gas generated upon combustion Use your answer in part (c)(i) and the following data to evaluate this hypothesis: Equation for combustion Relative rate of combustion Sucrose C 2 H 22 O (s) + 2O 2 (g) 2CO 2 (g) + H 2 O(g) Low Enthalpy of combustion / kj mol TNT 2C 7 H 5 N 3 O 6 (s) 7CO(g) + 7C(s) + 5H 2 O(g) + 3N 2 (g) High 3406 (3) (Total 7 marks) 7

8 5. But ene gas, burns in oxygen to produce carbon dioxide and water vapour according to the following equation. C 4 H 8 + 6O 2 4CO 2 + 4H 2 O (a) Use the data below to calculate the value of H Ө for the combustion of but--ene. Bond C C C=C C H O=O C=O O H Average bond enthalpy / kj mol (3) (b) State and explain whether the reaction above is endothermic or exothermic. (Total 4 marks) 8