Energy Changes in ReactionsIB MYP Chemistry: Topic test

20 questions, 54 marks

IB MYP Chemistry

Energy Changes in Reactions topic test

Total 54 marks

Name

Class

Date

1
A physiotherapist in Madrid uses an instant cold pack on a footballer's sprained ankle. When the pack is squeezed, ammonium nitrate dissolves in water inside the pack and the temperature falls from 22 °C to 4 °C.
(a)
What does the fall in temperature show about the dissolving?
[1 mark]
AIt is exothermic, because energy is released to the surroundings
BIt is a neutralisation reaction
CIt is endothermic, because energy is taken in from the surroundings
DNo energy change takes place, because energy is always conserved
(b)
On a reaction profile for the dissolving, how does the energy of the products compare with the energy of the reactants?
[1 mark]
AThe products are higher in energy
BThe products are lower in energy
CThe products and reactants are equal in energy
DIt depends on the activation energy
(c)
Explain why the pack feels cold when it is placed on the ankle.
[2 marks]
Total for question 1: 4 marks
2
A teacher in Sofia mixes 50 cm³ of dilute hydrochloric acid at 20.0 °C with 50 cm³ of sodium hydroxide solution at 20.0 °C in a polystyrene cup with a lid. The highest temperature reached is 26.5 °C. Assume that 100 g of solution is heated and that its specific heat capacity is 4.18 J g⁻¹ °C⁻¹.
(a)
Which row describes the reaction and gives the evidence?
[1 mark]
AEndothermic, because the temperature rose
BExothermic, because energy was transferred to the surroundings and the temperature rose
CEndothermic, because energy was transferred to the surroundings
DExothermic, because the temperature fell
(b)
Why is a polystyrene cup with a lid used instead of a metal can?
[1 mark]
APolystyrene conducts energy better than metal
BPolystyrene reacts with the acid
CThe lid stops the neutralisation from happening
DPolystyrene is a good insulator, so less energy is lost to the surroundings
(c)
Calculate the energy released in the reaction, in joules.
[2 marks]
Total for question 2: 4 marks
3
Students in Bogotá investigate how the concentration of copper(II) sulfate solution affects the temperature rise when it reacts with zinc: Zn + CuSO₄ → ZnSO₄ + Cu. In each trial they add 2.0 g of zinc powder to 50 cm³ of copper(II) sulfate solution in a polystyrene cup with a lid, stir, and record the highest temperature reached. Safety glasses are worn.
(a)
Write a hypothesis for this investigation, giving a scientific reason, and state one variable that must be kept constant.
[3 marks]
(b)
The temperature rises were 4.8 °C at 0.20 mol dm⁻³, 9.5 °C at 0.40 mol dm⁻³, 14.3 °C at 0.60 mol dm⁻³, 14.9 °C at 0.80 mol dm⁻³ and 15.0 °C at 1.00 mol dm⁻³. Describe the pattern in the results, explain why the temperature rise levels off at the highest concentrations, and suggest one improvement to the method.
[4 marks]
Total for question 3: 7 marks
4
A student in Auckland burns a peanut under a boiling tube containing 20.0 g of water. The water temperature rises from 21 °C to 64 °C and the peanut loses 0.60 g in mass. The packet says that peanuts release 25 kJ per gram. The student's country is considering a law that would require all packaged foods to show their energy content in kJ. (Specific heat capacity of water = 4.18 J g⁻¹ °C⁻¹.)
(a)
Calculate the energy released per gram of peanut, and evaluate the student's method, suggesting improvements.
[6 marks]
(b)
Discuss the benefits and drawbacks of requiring all packaged foods to show their energy content, and reach a justified conclusion.
[6 marks]
Total for question 4: 12 marks
5
A chef in Edinburgh cooks on a gas hob that burns methane: CH₄ + 2O₂ → CO₂ + 2H₂O. In a simple model, breaking all the bonds in the reactants for one mole of methane absorbs 2648 kJ, and forming all the bonds in the products releases 3466 kJ.
(a)
Which row gives the overall energy change for one mole of methane and the type of reaction?
[1 mark]
A+818 kJ, endothermic
B+6114 kJ, endothermic
C−6114 kJ, exothermic
D−818 kJ, exothermic
(b)
Which statement about bonds is correct?
[1 mark]
ABreaking bonds releases energy and making bonds absorbs energy
BBreaking bonds and making bonds both release energy
CBreaking bonds absorbs energy and making bonds releases energy
DBreaking bonds and making bonds both absorb energy
(c)
Use the energy values to explain why the burning of methane is exothermic.
[2 marks]
Total for question 5: 4 marks
6
A tea farm in Kericho, Kenya, grows tea plants and dries the leaves in a furnace that burns wood. In the leaves, photosynthesis uses sunlight to make glucose from carbon dioxide and water. A student models the furnace by burning a piece of wood under 250 g of water in a calorimeter. The burning wood releases 5000 J of energy into the water. (Specific heat capacity of water = 4.18 J g⁻¹ °C⁻¹.)
(a)
Why is photosynthesis described as an endothermic reaction?
[1 mark]
AIt takes in energy from the surroundings in the form of sunlight
BIt releases energy to the surroundings as heat
CIt does not involve any energy change
DIt needs a spark and then keeps going on its own
(b)
Which process is exothermic?
[1 mark]
APhotosynthesis in the tea leaves
BBurning wood in the furnace
CThermal decomposition of limestone to make lime
DDissolving ammonium nitrate to make a cold pack
(c)
Calculate the temperature rise of the water in the model.
[2 marks]
Total for question 6: 4 marks
7
An engineering student in Quito studies how charcoal, which is almost pure carbon, burns in a barbecue: C + O₂ → CO₂. In a simple model for one mole of carbon, the reactants have an energy of 500 kJ, the highest point on the reaction profile is at 620 kJ and the products have an energy of 106 kJ.
(a)
Calculate the activation energy and the overall energy change, and state whether the reaction is exothermic or endothermic.
[3 marks]
(b)
Charcoal does not burn until it is lit, even though burning releases energy. Use the energy values to explain why it must be lit and why it keeps burning once it has been lit.
[4 marks]
Total for question 7: 7 marks
8
A district heating plant in Sweden burns wood pellets, made from sawmill waste, to heat water for homes. Burning wood pellets releases about 17 kJ per gram. Burning natural gas releases about 55 kJ per gram, but it releases carbon dioxide from fossil carbon. The plant manager is deciding whether to switch some of the boilers from natural gas to wood pellets. (Specific heat capacity of water = 4.18 J g⁻¹ °C⁻¹.)
(a)
Calculate the mass of wood pellets and the mass of natural gas needed to raise the temperature of 2000 g of water by 50 °C, assuming all the energy is transferred to the water. Compare your answers.
[6 marks]
(b)
Discuss the benefits and drawbacks of switching some boilers from natural gas to wood pellets, and reach a justified conclusion.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).