Energy Changes in Chemistry

(i) Draw a labelled energy diagram for the evaporation of freon-11, showing reactants, products, and the change in enthalpy (ΔrH).

(ii) By referring to both the change in enthalpy and the attractive forces between particles in freon-11, explain how this process can be used to cool down a refrigerator.

(i) Use the change in enthalpy (ΔrH°) for the reaction above and the bond energies listed in the table below to calculate the average bond energy of the C–Cl bond.

Calculate the amount of energy released when 126 g of ozone, O3(g), is decomposed into oxygen gas, O2(g). M(O3) = 48.0 g mol–1.

(i) Classify this process as exothermic or endothermic, with a reason.

(ii) The equation for the dissolving of solid potassium bromide, KBr(s), in water, is shown below. KBr(s) → K+(aq) + Br–(aq) ΔrH = +19.9 kJ mol–1 Both lithium bromide, LiBr(s), and solid potassium bromide, KBr(s), are dissolved in 200 mL of water, in separate beakers. 20.0 g of LiBr is dissolved in the first beaker, resulting in an energy change. Calculate the mass of solid potassium bromide, KBr(s), that would need to be dissolved in the second beaker in order to have an energy change of equal magnitude (size). M(LiBr) = 86.8 g mol–1 M(KBr) = 119 g mol–1.

(iii) By considering the enthalpy change of each process, explain any difference in the resultant temperatures of each solution. No calculations are needed in your answer.

(i) Which diagram below best represents the reaction profile for this chemical reaction? Circle one: Diagram A Diagram B Explain your answer.

(ii) On the diagram that you chose above, clearly label the change in enthalpy (∆rH).

Calculate the energy produced by the combustion of this amount of kerosene fuel. M(C12H26) = 170 g mol–1.