5. Chemical energetics
A section of Chemistry, 9701
Listing 10 of 306 questions
A neutralisation reaction occurs when NaOHis added to H2SO4. equation 1 2NaOH+ H2SO4Na2SO4+ 2H2ODefine enthalpy change of neutralisation, ∆Hneut. An experiment is carried out to calculate ∆Hneut for the reaction between NaOHand H2SO4. 100 cm3 of 1.00 mol dm–3 NaOHis added to 75 cm3 of 1.00 mol dm–3 H2SO4in a polystyrene cup and stirred. Results from the experiment are shown in Table 2.1. Table 2.1 initial temperature of NaOH/ °C 20.0 initial temperature of H2SO4/ °C 20.0 maximum temperature of mixture / °C 27.8 Use equation 1 to calculate the amount, in mol, of H2SO4that is neutralised in the experiment. amount of H2SO4neutralised = mol Calculate ∆Hneut using the results in Table 2.1. Include units in your answer. Assume that: • the specific heat capacity of the final solution is 4.18 J g–1 K–1 • 1.00 cm3 of the final solution has a mass of 1.00 g • there is no heat loss to the surroundings • full dissociation of H2SO4occurs • the experiment takes place at constant pressure. Show your working. ∆Hneut = units Complete the equation for the reaction that occurs when a solution of Ba(OH)2 is added to aqueous sulfuric acid. Include state symbols. H2SO4+ Ba(OH)2………………………………………………………… Suggest why the enthalpy change of neutralisation cannot be determined using the addition of dilute sulfuric acid to aqueous barium hydroxide.
9701_s23_qp_21
THEORY
2023
Paper 2, Variant 1
View
A neutralisation reaction occurs when NaOHis added to H2SO4. equation 1 2NaOH+ H2SO4Na2SO4+ 2H2ODefine enthalpy change of neutralisation, ∆Hneut . In an experiment, 50.0 cm3 of 2.00 mol dm–3 NaOHis added to 60.0 cm3 of 1.00 mol dm–3 H2SO4in a polystyrene cup and stirred. Both solutions have a temperature of 21.4 °C before mixing. The maximum temperature of the mixture is measured. Use equation 1 to calculate the amount, in mol, of H2SO4that is neutralised in the experiment. amount of H2SO4 neutralised = mol Calculate the theoretical maximum temperature of the mixture in this experiment. Assume that: • enthalpy change of neutralisation, ∆Hneut , of NaOHand H2SO4is –57.1 kJ mol–1 • full dissociation of H2SO4occurs • the specific heat capacity of the final solution is 4.18 J g–1 K–1 • 1.00 cm3 of the final solution has a mass of 1.00 g • there is no heat loss to the surroundings • the experiment takes place at constant pressure. Show your working. theoretical maximum temperature = °C The enthalpy change of neutralisation of CH3COOHand NaOHis –55.2 kJ mol–1. Complete the equation for the reaction. CH3COOH + NaOH Values for the enthalpy change of neutralisation, ∆Hneut , are shown in Table 3.1. Table 3.1 reagents ∆Hneut / kJ mol–1 NaOH + HCl –57.1 NaOH + CH3COOH –55.2 Suggest why the value for ∆Hneut of the weak acid, CH3COOH, reacting with NaOH is different to the value obtained using the strong acid, HCl. Assume that the values are determined under the same conditions.
9701_s23_qp_23
THEORY
2023
Paper 2, Variant 3
View
Complete Table 8.1 by placing one tick (✓) in each row to indicate the sign of each type of energy change under standard conditions. Table 8.1 energy change always positive always negative can be either negative or positive lattice energy enthalpy change of hydration enthalpy change of solution Define enthalpy change of hydration. Table 8.2 shows various energy changes which can be used in the following questions. Table 8.2 energy change value / kJ mol–1 standard enthalpy change of atomisation of calcium +178.2 first ionisation energy of calcium +590 second ionisation energy of calcium +1145 standard enthalpy change of atomisation of bromine +111.9 Br–Br bond energy +192.9 standard enthalpy change of solution of calcium bromide, CaBr2–103.1 standard enthalpy change of formation of calcium bromide, CaBr2–682.8 standard enthalpy change of hydration of Ca2+ –1579 first electron affinity of bromine –324.6 first ionisation energy of bromine +1140 Select and use relevant data from Table 8.2 to calculate the lattice energy, ΔH o latt, of CaBr2. It may be helpful to draw a labelled energy cycle. Show your working. ΔH o latt of CaBr2= kJ mol–1 Select and use relevant data from Table 8.2 and your answer to to calculate the standard enthalpy change of hydration, ΔH o hyd, of Br –. It may be helpful to draw a labelled energy cycle. If you were not able to answer , use –2500 kJ mol–1 as your value for ΔH o latt of CaBr2. This is not the correct value. Show your working. ΔH o hyd of Br – = kJ mol–1 The enthalpy change of hydration of the Br – ion is more negative than the enthalpy change of hydration of the I– ion. Explain why.
9701_s23_qp_41
THEORY
2023
Paper 4, Variant 1
View
Complete Table 8.1 by placing one tick (✓) in each row to indicate the sign of each type of energy change under standard conditions. Table 8.1 energy change always positive always negative can be either negative or positive lattice energy enthalpy change of hydration enthalpy change of solution Define enthalpy change of hydration. Table 8.2 shows various energy changes which can be used in the following questions. Table 8.2 energy change value / kJ mol–1 standard enthalpy change of atomisation of calcium +178.2 first ionisation energy of calcium +590 second ionisation energy of calcium +1145 standard enthalpy change of atomisation of bromine +111.9 Br–Br bond energy +192.9 standard enthalpy change of solution of calcium bromide, CaBr2–103.1 standard enthalpy change of formation of calcium bromide, CaBr2–682.8 standard enthalpy change of hydration of Ca2+ –1579 first electron affinity of bromine –324.6 first ionisation energy of bromine +1140 Select and use relevant data from Table 8.2 to calculate the lattice energy, ΔH o latt, of CaBr2. It may be helpful to draw a labelled energy cycle. Show your working. ΔH o latt of CaBr2= kJ mol–1 Select and use relevant data from Table 8.2 and your answer to to calculate the standard enthalpy change of hydration, ΔH o hyd, of Br –. It may be helpful to draw a labelled energy cycle. If you were not able to answer , use –2500 kJ mol–1 as your value for ΔH o latt of CaBr2. This is not the correct value. Show your working. ΔH o hyd of Br – = kJ mol–1 The enthalpy change of hydration of the Br – ion is more negative than the enthalpy change of hydration of the I– ion. Explain why.
9701_s23_qp_43
THEORY
2023
Paper 4, Variant 3
View
Define enthalpy change of formation. Iron is made when iron(oxide is heated with carbon monoxide, as shown by reaction 2. reaction 2 Fe2O3 + 3CO 2Fe + 3CO2 Table 4.1 shows enthalpy change of formation data measured at 298 K and 101 kPa. Table 4.1 substance equation value for ∆H f o / kJ mol–1 Fe2O3 –824.2 CO –110.5 CO2 C+ O2CO2–393.5 Complete Table 4.1 by adding equations with relevant state symbols to represent: • standard enthalpy change of formation for Fe2O3 • standard enthalpy change of formation for CO. Use the data in Table 4.1 to calculate the enthalpy change of reaction, ∆Hr , in kJ mol–1, for reaction 2. Show your working. ∆Hr = kJ mol–1
9701_s24_qp_21
THEORY
2024
Paper 2, Variant 1
View
Separate samples of Na2CO3 and NaHCO3 react with HCl to produce the same products, as shown in Table 2.1. Table 2.1 reaction equation ∆H / kJ mol–1 Na2CO3 + 2HCl 2NaCl + H2O + CO2 ∆H1 NaHCO3 + HCl NaCl + H2O + CO2 ∆H2 = +27.2 Complete the reaction pathway diagram in for reaction 2. Label the diagram to show the enthalpy change, ∆H2, and the activation energy, EA. NaHCO3 + HCl energy / kJ mol–1 progress of reaction The value for ∆H1 is determined by experiment using the following method. • 50.0 cm3 of 2.00 mol dm–3 HCl 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. 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 Thermal decomposition occurs when NaHCO3 is heated. reaction 3 2NaHCO3 Na2CO3 + H2O + CO2 Calculate the enthalpy change for reaction 3, ∆Hr , using the data in Table 2.1 and the value of ∆H1 calculated in . (If you were unable to calculate a value for ∆H1 in , assume the enthalpy change is –38.4 kJ mol–1. This is not the correct value.) ∆Hr = kJ mol–1 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. , ,
9701_s24_qp_22
THEORY
2024
Paper 2, Variant 2
View
Questions Discovered
306