Separate samples of Na2CO3 and NaHCO3 react with HCl(aq) to produce the same products, as shown in Table 2.1. Table 2.1 reaction equation ∆H/kJ mol-1 1 Na2CO3 + 2HCl → 2NaCl + H2O + CO2 ∆H1 2 NaHCO3 + HCl → NaCl + H2O + CO2 ∆H2 = +27.2

1. (a)Complete the reaction pathway diagram in Fig. 2.1 for reaction 2. Label the diagram to show the enthalpy change, ∆H2, and the activation energy, EA. energy /kJ mol-1 NaHCO3 + HCI progress of reaction Fig. 2.1[2]
2. (b)(i)The value for ∆H1 is determined by experiment using the following method. • 50.0 cm³ of 2.00 mol dm⁻³ HCl(aq) is added to a polystyrene cup. • The initial temperature of the acid is recorded as 19.6°C. • 0.0400 mol of Na2CO3 is added and the mixture is stirred. • All the solid Na2CO3 disappears and a colourless solution is produced. The maximum temperature recorded during the reaction is 26.2°C. Describe one other observation that shows the reaction is complete.[1]
3. (b)(ii)Calculate the value of ∆H1 in kJ mol⁻¹. Assume the specific heat capacity of the reaction mixture is the same as for water and no heat is lost to the surroundings. Show your working. ∆H1 = ............................ kJ mol⁻¹[3]
4. (b)(iii)Thermal decomposition occurs when NaHCO3 is heated. reaction 3 2NaHCO3 → Na2CO3 + H2O + CO2 Calculate the enthalpy change for reaction 3, ∆H3, using the data in Table 2.1 and the value of ∆H1 calculated in (b)(ii). (If you were unable to calculate a value for ∆H1 in (b)(ii), assume the enthalpy change is –38.4 kJ mol⁻¹. This is not the correct value.) ∆H3 = ............................ kJ mol⁻¹[2]
5. (c)Z is a salt that contains a Period 4 element from Group 2. When Z is heated brown gas forms. Identify the formula of Z and use it to write an equation for the reaction.[2]

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