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2 marksEnergetics

CSEC Chemistry · January 2018 · Paper 2 · Question 4(b)(ii)

In an experiment, when 12.0 g of potassium nitrate, KNO₃, is dissolved in 100 cm³ of water, the temperature drops by 4.20 °C.

Calculate the heat change for the reaction. Specific heat capacity of water = 4.2 J g⁻¹ °C⁻¹; Heat change = m × c × △T; Density of water = 1 g cm⁻³

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  1. 4(a)(i)Distinguish between the terms 'endothermic' and 'exothermic.'[2 marks]
  2. 4(a)(ii)Generally, when chemical reactions take place, existing bonds are broken and new bonds are formed. Classify bond making AND bond breaking as either endothermic…[1 mark]
  3. 4(b)(i)Calculate the number of moles of KNO₃ used in the experiment. (RMM: KNO₃ = 101)[1 mark]
  4. 4(b)(iii)Calculate the enthalpy change for 1 mole of potassium nitrate.[1 mark]
  5. 4(b)(iv)List TWO pieces of apparatus necessary to conduct the experiment in a school laboratory. State how EACH piece of apparatus is used.[4 marks]
  6. 4(b)(v)Draw a labelled energy profile diagram to represent the enthalpy change for the reaction. On your diagram, indicate the sign of △H for the reaction.[3 marks]

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