5. Chemical energetics
A section of Chemistry, 9701
Listing 10 of 306 questions
Entropy is a measure of the disorder of a system. Assume the entropy, S, for H2O is zero at 0 K. Sketch a graph on the axes to show how the entropy changes for H2O between 0 K and 300 K. S / J K–1 mol–1 temperature / K  Place one tick () in each row of the table to show the sign of the entropy changes, ΔS. ΔS is negative ΔS is positive solid dissolving in water water boiling to steam  The equation for a reaction that produces methanol is shown. CO2+ 3H2CH3OH+ H2OUse relevant bond energies from the Data Booklet to calculate the enthalpy change, ΔH, for this gas phase reaction. ΔH = kJ mol–1 At 298 K, both products of this reaction are liquid. CO2+ 3H2CH3OH+ H2OΔH o = –131 kJ mol–1 Standard entropies are shown in the table. substance CO2H2CH3OHH2OS o / J K–1 mol–1 +214 +131 +127 +70 Calculate the standard entropy change, ΔS o, for this reaction. ΔS o = J K–1 mol–1 Calculate the standard Gibbs free energy change, ΔG o, for this reaction at 298 K. ΔG o = kJ mol–1 Predict the effect of increasing the temperature on the feasibility of this reaction. In a methanol-oxygen fuel cell, CH3OHand O2are in contact with two inert electrodes immersed in an acidic solution. The half-equation for the reaction at the methanol electrode is shown. CH3OH + H2O CO2 + 6H+ + 6e– E o = – 0.02 V Use the Data Booklet to write an equation for the overall cell reaction. Use E o values to calculate the for this reaction.  = V 
9701_w18_qp_41
THEORY
2018
Paper 4, Variant 1
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Entropy is a measure of the disorder of a system. Assume the entropy, S, for H2O is zero at 0 K. Sketch a graph on the axes to show how the entropy changes for H2O between 0 K and 300 K. S / J K–1 mol–1 temperature / K  Place one tick () in each row of the table to show the sign of the entropy changes, ΔS. ΔS is negative ΔS is positive solid dissolving in water water boiling to steam  The equation for a reaction that produces methanol is shown. CO2+ 3H2CH3OH+ H2OUse relevant bond energies from the Data Booklet to calculate the enthalpy change, ΔH, for this gas phase reaction. ΔH = kJ mol–1 At 298 K, both products of this reaction are liquid. CO2+ 3H2CH3OH+ H2OΔH o = –131 kJ mol–1 Standard entropies are shown in the table. substance CO2H2CH3OHH2OS o / J K–1 mol–1 +214 +131 +127 +70 Calculate the standard entropy change, ΔS o, for this reaction. ΔS o = J K–1 mol–1 Calculate the standard Gibbs free energy change, ΔG o, for this reaction at 298 K. ΔG o = kJ mol–1 Predict the effect of increasing the temperature on the feasibility of this reaction. In a methanol-oxygen fuel cell, CH3OHand O2are in contact with two inert electrodes immersed in an acidic solution. The half-equation for the reaction at the methanol electrode is shown. CH3OH + H2O CO2 + 6H+ + 6e– E o = – 0.02 V Use the Data Booklet to write an equation for the overall cell reaction. Use E o values to calculate the for this reaction.  = V 
9701_w18_qp_43
THEORY
2018
Paper 4, Variant 3
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Questions Discovered
306