Energy level diagrams and bond energyIB MYP Chemistry: Mind map

Exam questions on Energy level diagrams and bond energy

1. A camping stove burns butane gas. Butane does not catch fire by itself when it leaves the canister. The user has to press a button that makes a spark, and after that the flame keeps burning and releases a lot of heat.
   Explain why a spark is needed to start the reaction even though the reaction releases energy overall.2 marks
2. Hydrogen gas reacts with chlorine gas to make hydrogen chloride: H₂ + Cl₂ → 2HCl. Breaking the bonds in one mole of hydrogen molecules and one mole of chlorine molecules takes in a total of 679 kJ. Making the bonds in two moles of hydrogen chloride releases a total of 864 kJ.
   Use the data to work out the overall energy change for this reaction and state whether it is exothermic or endothermic.2 marks
3. Students at a school in Cairo want to find out whether the reaction between citric acid solution and sodium hydrogencarbonate powder is exothermic or endothermic. They plan to add 5 g of sodium hydrogencarbonate to 50 cm³ of citric acid solution in a polystyrene cup with a lid, stir the mixture and record the temperature.
   Before the experiment the students made a hypothesis. Write a suitable hypothesis for the temperature change, giving a scientific reason.3 marks