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Unit 3 PPA 1 Verification of Hess’s Law

Unit 3 PPA 1 Verification of Hess’s Law. Verification of Hess’s Law (Unit 3 PPA 1). The aim of the experiment is to show that the enthalpy change for a reaction is independent of the reaction pathway.

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Unit 3 PPA 1 Verification of Hess’s Law

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  1. Unit 3 PPA 1 Verification of Hess’s Law

  2. Verification of Hess’s Law (Unit 3 PPA 1) The aim of the experiment is to show that the enthalpy change for a reaction is independent of the reaction pathway. The diagram below shows how potassium chloride can be formed from potassium hydroxide by two different reaction pathways. KOH(aq) 1 DH1 2 DH2 DH3 KOH(s) KCl(aq) 3 (1) Name the chemicals shown by the numbers 1,2 and 3. (1) 1 is water, 2 and 3 are hydrochloric acid. (2) What is the relationship between DH1, DH2 andDH3 if the enthalpy of a reaction is independent of the reaction pathway? (2) DH3 = DH1 + DH2

  3. Mass of mixed solution (potassium hydroxide solution and hydrochloric acid) Average temperature of solutions (KOH(aq) and HCl(aq) before mixing. The diagram below shows how potassium chloride can be formed from potassium hydroxide by two different reaction pathways. KOH(aq) 1 DH1 2 DH2 DH3 KOH(s) KCl(aq) 3 Highest temperature of mixed solutions. (3) Complete the list of measurements that would have to be made in order to calculate DH2. (i) Mass of potassium hydroxide (ii) ……………………………………………………………………………………………………………………………………….. (iii) ……………………………………………………………………………………………………………………………….…….. (iv) …………………………………………………………………………………………………………………………………….. • In the determination DH3 of the following results were obtained:- • When 1.4g of potassium hydroxide is added to 50cm3 of 1 mol l-1 • hydrochloric acid the temperature rose from 21.5oC to 27.7oC. • Calculate the value for the enthalpy change, DH3. (4) DH = - cmDT = - 4.18 x 0.05 x 6.2 = - 1.296 kJ

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