CHEM 210 MODULE 3 EXAM QUESTIONS AND CORRECT ANSWERS, WITH COMPLETE SOLUTION 2024.

CHEM 210 MODULE 3 EXAM QUESTIONS AND CORRECT ANSWERS, WITH COMPLETE SOLUTION 2024. What is meant by the term average bond enthalpy? (Average enthalpy change) when one mole of bonds of (gaseous covalent) bonds is broken The calculated value of ΔHc from this experiment is different from the value obtained from data books. Apart from heat loss, suggest two reasons for the difference. Assume that the calculation has been carried out correctly. incomplete combustion non-standard conditions evaporation of alcohol/water specific heat capacity of beaker/apparatus The enthalpy change of combustion for alcohol J can also be determined indirectly from standard enthalpy changes of formation. (i) Write an equation, including state symbols, for the chemical change that represents the standard enthalpy change of formation of the liquid alcohol J, C5H12O. 5C(s) + 6H2(g) + 1⁄2O2(g) ⎯→ C 5H12O(l) A closed system is required for dynamic equilibrium to be established. State one other feature of this dynamic equilibrium. Rate of the forward reaction is equal to the rate of the reverse reaction OR concentrations do not change The student heats the equilibrium mixture keeping the volume constant. Predict how the composition of the equilibrium mixture changes on heating. Explain your answer. More H2 and I2 OR less HI (equilibrium position shifts) to the left AND (Forward) reaction is exothermic OR reverse reaction is endothermic OR in the endothermic direction A student mixes hydrogen and iodine at room temperature and pressure and allows the mixture to reach dynamic equilibrium. H2(g) + I2(g) 2HI(g) ΔH = −9 kJ mol−1 equilibrium 3.1 Predict and explain what effect, if any, an increase in the pressure would have on the position of the equilibrium. effect .................................................................................................................................. explanation ............................................................ No effect AND Same number of (gaseous) moles on both sides ............................................................ What is meant by the term standard enthalpy change of formation? Give the standard conditions. (Enthalpy change) when one mole of a compound is formed from its elements 298 K / 25 °C AND 1 atm / 100 kPa / 101 kPa / 1 bar Describe and explain, using equations, how the concentration of ozone in the stratosphere is maintained. O3 O2 + O AND O + O2 O3 rate of ozone decomposition (almost) equals rate of ozone formation In the stratosphere, NO catalyses the breakdown of ozone. Write two equations to show how NO catalyses this breakdown. NO + O.3 NO2 + O2 NO2 + O NO + O2 It is not possible to measure the enthalpy change of formation of N2O(g) directly. Suggest why it is not possible. It is very difficult to determine the standard enthalpy change of formation of hexane directly. Suggest a reason why. Reaction gives NO OR reaction gives NO2 OR reaction gives a mixture of oxides OR activation energy too high OR rate of reaction is too slow Methane is a greenhouse gas. Scientists are concerned that the concentration of methane in the atmosphere is slowly increasing. (i) Explain how atmospheric methane molecules can contribute to global warming. Absorbs IR radiation Bonds vibrate One way that scientists hope to minimise global warming is by developing Carbon Capture and Storage, CCS, techniques. Describe two of these CCS techniques. (liquid) injected deep into the oceans