EJC Prelim H2 Chemistry Paper 2 Solution

1 © EJC 9729/02/J2Prelim/25 1 Mount Ijen in East Java is famous for its rare blue flames, visible at night. The phenomenon occurs when sulfur vapour , from the volcano’s cracks burns, producing bright blue flames and sulfur dioxide. In the cool high -altitude air, some of the vapour condenses into solid sulfur. (a) A team of environmental chemists were authorised to collect solid sulfur deposits near Mount Ijen’s crater to investigate volcanic activity. The chemists burnt the sulfur sample and measured the temperature change for a fixed amount of water placed in a calorimeter. The data from their experiment is shown in Table 1.1. Table 1.1 mass of solid sulfur powder burnt /g 0.76 mass of water in beaker /g 150 initial temperature of water /oC 29.8 final temperature of water / oC 39.7 (i) Construct an equation to represent the standard enthalpy change of combustion of solid sulfur, S. ................................ ................................ ................................ ...................... [1] (ii) Calculate the enthalpy change of combustion of solid sulfur , S, based on their experiment. [2] EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2025 General Certificate of Education Advanced Level Higher 2 Chemistry Paper 2 Suggested Solutions with Marker’s comments ( )150 4.18 39.7 29.8 6207.3 J q mc T=−  =−   − =− 1 1 6207.3 0.76 32.1 262176 J mol 262 kJ mol qH n − − − = = =− =− S (s) + O2 (g) → SO2 (g)

2 © EJC 9729/02/J2Prelim/25 (iii) During volcanic activity, many sulfur-containing gases such as hydrogen sulfide, H2S, and sulfur dioxide, SO2, are released. In the atmosphere, H2S can oxidise to form SO2, and subsequently sulfur trioxide, SO3, may be formed. H2S(g) + 3/2 O2(g) → SO2(g) + H2O(l) ∆Hr = –562 kJ mol–1 Use the data given in Table 1.2 to calculate the enthalpy change of combustion of solid sulfur, S. Table 1.2 compound ∆Hf / kJ mol–1 H2S(g) –20.6 H2O(l) –285.8 [2] (iv) Comment on the difference in values for the enthapy change of combustion of solid sulfur determined in (a)(ii) and (a)(iii). ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ...................... [1] (v) With reference to a relevant chemical equation, explain how the release of sulfur-containing gases during volcanic activity can have a negative impact on the environment. ................................ ................................ ................................ ........................... ................................ ................................ ...........................