5 marksHigher
A container holds 1.5 dm³ of a solution with concentration 8.0 g/dm³. The solvent evaporates and 1.0 dm³ remains. No solute is lost.
.1Calculate the final concentration.
[3 marks] .2Explain why the concentration changes even though no solute is added.
[2 marks] 4 marksHigher
A pupil estimates the energy change for
CH4+Cl2→CH3Cl+HCl. Bond energies are C-H 413, Cl-Cl 243, C-Cl 338 and H-Cl 431 kJ/mol.
.1Calculate the energy change using only bonds that change.
[3 marks] .2Evaluate the claim that breaking the C-H bond supplies the energy released.
[1 mark] 5 marksFoundation and Higher
A steel object of mass 45.0 g is left in damp air. After all loose material is retained, the object and corrosion products have mass 47.7 g.
.1Calculate the percentage increase in mass.
[3 marks] .2Explain why the increase does not contradict conservation of mass.
[2 marks] 4 marksHigher
A catalyst changes the highest point of a reaction profile from 170 kJ to 115 kJ. Reactants remain at 40 kJ and products at 15 kJ.
.1Calculate the catalysed activation energy.
[2 marks] .2Evaluate the statement: "The catalyst releases an extra 55 kJ, so the reaction becomes more exothermic."
[2 marks] 4 marksFoundation and Higher
Three noble gases have boiling points: helium −269 °C, neon −246 °C and argon −186 °C.
.1Calculate the rise in boiling point from helium to argon.
[2 marks] .2Describe the trend and predict whether krypton, below argon, boils above or below −186 °C.
[2 marks] 