26 questions · 198 marks · ≈ 3 hours
Which is true about chemical energy changes?
| Reaction type | Energy flows | Temperature of surroundings | |
|---|---|---|---|
| A | exothermic | to the surroundings | increases |
| B | exothermic | from the surroundings | decreases |
| C | endothermic | to the surroundings | decreases |
| D | endothermic | from the surroundings | increases |
Choose your answer
Which statement is true about exothermic and endothermic reactions?
Choose your answer
The products have more energy than the reactants in an exothermic reaction
The products have more energy than the reactants in an endothermic reaction
The activation energy for an exothermic reaction is always larger than the activation energy for an endothermic reaction
Most reactions are endothermic
When solid sodium oxide is added to water, an exothermic reaction occurs:
Na2O (s) + H2O (l)2NaOH (aq)
A student uses the apparatus below to measure the temperature change of the reaction:
The student records the following results for the reaction:
mass of sodium oxide used = 3.0 g
volume of water used = 50 cm3
starting temperature of mixture = 19.5 oC
maximum temperature of mixture = 30.5 oC
What is the heat energy, Q, released in this experiment, in J?
c = 4.2 J/g/ oC
mass of 1 cm3 of water = 1 g
Choose your answer
Q = 2,310 J
Q = 2,450 J
Q = 139 J
Q = 126 J
The graph below shows a reaction profile for the reaction between methane and oxygen.
What does the label X represent?
Choose your answer
Activation Energy
Overall energy change
Reactants
Progress of the reaction
The reaction profile for making nitrogen monoxide, NO, is shown below:
What is the activation energy for this reaction?
Choose your answer
+140 kJ
+180 kJ
+320 kJ
-330 kJ
A student uses this apparatus to investigate the heat energy change when a salt dissolves in water to form a solution.
This is the student’s method.
i) Name the piece of apparatus the student should use to add the distilled water to the polystyrene cup.
(1 mark)
ii) The student stirs the solution to help the solid dissolve more quickly.
Suggest another reason why the student stirs the solution.
(1 mark)
iii) State the colour of the copper(II) sulfate solution.
(1 mark)
The diagram shows the temperatures in one experiment.
Complete the table, giving all values to the nearest 0.1 °C.
| maximum temperature in °C | |
|---|---|
| initial temperature in °C | |
| increase in temperature in °C |
In a second experiment, when a student dissolves the anhydrous copper(II) sulfate in 50 cm3 of distilled water, the increase in temperature is 3.3 °C.
i) Show that the heat energy change (Q) in this second experiment is approximately 700 J.
[for water, c = 4.2 J / g / °C]
[mass of 1.0 cm3 of water = 1.0 g]
(2 marks)
ii) In this experiment, the student uses 1.70 g of the anhydrous copper(II) sulfate.
Calculate the molar enthalpy change (ΔH) in kJ / mol.
Include a sign in your answer.
[Mr of CuSO4 = 159.5]
(4 marks)
ΔH = ................................ kJ / mol
Another student does a similar experiment but uses hydrated copper(II) sulfate instead of anhydrous copper(II) sulfate.
The table shows his results.
| initial temperature in °C | 23.8 |
|---|---|
| final temperature in °C when all solid dissolves | 22.7 |
Explain what the results show about the type of energy change that occurs when hydrated copper(II) sulfate dissolves.
A student uses this apparatus to investigate the temperature change that occurs when ammonium nitrate is dissolved in water.
She uses this method.
The table shows her results.
| Initial temperature of water inoC | 20.0 |
|---|---|
| Lowest temperature of solution inoC | 14.2 |
Use the results of the experiment to explain what type of reaction is taking place when ammonium nitrate is added to water.
Show that the heat energy change, Q, is about 2400 J.
[mass of 1.00 cm3 of solution = 1.00 g]
[for the solution, c = 4.185 J / g / °C]
*Q *= .............................. J
Use your answer to part (b) to calculate the enthalpy change, ΔH, in kilojoules per mole of ammonium nitrate.
[Mr of ammonium nitrate = 80.0]
Include a sign in your answer.
ΔH = .............................. kJ / mol
Sodium oxide reacts with water to form sodium hydroxide.
A scientist plans to measure the temperature change of the reaction using calorimetry in a lab.
This is the scientist's basic method:
Which apparatus list is the most appropriate for this experiment?
Choose your answer
Electronic balance, measuring cylinder, glass beaker, thermometer
Measuring cylinder, glass beaker, polystyrene cup, thermometer
Electronic balance, glass beaker, polystyrene cup, thermometer
Measuring cylinder, glass beaker, glass rod, thermometer
A student uses this apparatus to investigate the heat energy released when a liquid fuel is burned.
This is the student’s method.
Suggest why the student measures the mass of the spirit burner and fuel immediately after heating the water.
When the fuel is burned, the student notices that a black solid forms on the bottom of the copper can.
i) Identify the black solid.
(1 mark)
ii) Explain why the black solid forms.
(2 marks)
i) Show that the heat energy change, Q, to raise the temperature of 100 cm3 of water by 30 °C is approximately 13 kJ.
[mass of 1.0 cm3 of water = 1.0 g] [c for water = 4.2 J / g / °C]
(3 marks)
ii) The student burns 0.96 g of methanol, CH3OH Calculate the molar enthalpy change, ΔH, in kJ / mol, for the combustion of methanol. Include a sign in your answer. [Mr of methanol = 32]
(3 marks)
ΔH = ...................................................................... kJ / mol
The table shows data book values for the molar enthalpy change, ΔH, for the combustion of some alcohols with different numbers of carbon atoms per molecule.
| Number of carbon atoms per molecule | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Molar enthalpy change, ΔH , in kJ/mol | -730 | -1370 | -2020 | -2680 | -3320 |
i) Plot the data values from the table on the grid. Draw a straight line of best fit.
(2 marks)
ii) Deduce the value of ΔH for an alcohol with six carbon atoms per molecule. Show on the graph how you obtained your answer.
(2 marks)
ΔH = ...................................................................... kJ/mol
iii) State the relationship between ΔH and the number of carbon atoms per molecule.
(1 mark)
This question is about lithium oxide.
The diagram shows the electron configurations of an atom of lithium and an atom of oxygen.
Describe the changes in electronic configuration when lithium and oxygen react to form lithium oxide, Li2O
Lithium oxide reacts with water to form lithium hydroxide as the only product. A scientist uses this apparatus to measure the temperature change of the reaction.
This is the scientist’s method.
The diagram shows the thermometer readings before and after adding the lithium oxide.
i) Complete the table, giving all values to the nearest 0.1 °C.
(2 marks)
| temperature in °C after adding the lithium oxide | |
|---|---|
| temperature in °C before adding the lithium oxide | 17.3 |
| temperature rise in °C |
ii) Calculate the heat energy change in the reaction. Give your answer to two significant figures. [c = 4.2 J / g / °C]
(4 marks)
heat energy change = .............................. J
iii) In another experiment the scientist obtains these results.
| amount of lithium oxide in mol | 0.0580 |
|---|---|
| heat energy change in J | 5210 |
Calculate the molar enthalpy change (ΔH) in kJ / mol. Include a sign in your answer.
(3 marks)
ΔH = ..............................kJ / mol
iv) Give a reason why the scientist does the experiment in a polystyrene cup.
(1 mark)
Another student carries out the experiment to find the heat energy released in the reaction of sodium oxide with water:
Na2O (s) + H2O (l) 2NaOH (aq)
They found that 10,800 J of heat energy was released when 0.060 mol of sodium oxide reacts.
What is the value of ΔH, in kJ/mol, for the reaction of sodium oxide with water?
Choose your answer
0.0056 kJ/mol
180 kJ/mol
1,800 kJ/mol
8,000 kJ/mol
The actual molar enthalpy change, ΔH, for the reaction of sodium oxide with water, is -238 kJ/mol.
Experimental results from calorimetry in labs give less exothermic results.
Which of the following does not explain this difference?
Choose your answer
The reaction may have been incomplete
Heat energy also transfers to the surroundings
The calorimetry equipment also has a specific heat capacity, and so affects the final temperature reading
The student measured the initial temperature of the water as lower than the actual value.
A student investigates the reaction between zinc and copper(II) sulfate solution. The equation for the reaction is
Zn + CuSO4 → Cu + ZnSO4
This is his method.
i) Suggest why it is not important to add an exact mass of zinc powder.
(1 mark)
ii) State the colour change of the solution. from ........................................................... to ...........................................................
(2 marks)
The table shows the student’s results
| volume of copper(II) sulfate solution in cm3 | 25.0 |
|---|---|
| initial temperature of copper(II) sulfate solution in °C | 19.0 |
| final temperature of solution in °C | 31.5 |
i) Show that the heat energy change (Q) is about 1300 J. [for the solution, c = 4.18 J/g/°C] [mass of 1.00 cm3 of solution = 1.00 g]
(3 marks)
ii) The mass of anhydrous copper(II) sulfate (CuSO4) used to make 25.0 cm3 of solution is 2.00 g. Calculate the amount, in moles, of CuSO4 in 2.00 g. [Mr of CuSO4 = 159.5]
(1 mark)
iii) Calculate the value of the enthalpy change (ΔH), in kilojoules per mole, for the reaction between zinc and copper(II) sulfate. Include a sign in your answer.
(3 marks)
During the Second World War, engineers developed a rocket-powered aircraft.
The aircraft carried these two liquids
When these two liquids mix in the combustion chamber, they evaporate and then react rapidly to form nitrogen gas, N2, and steam, H2O
The reaction is exothermic.
The equation for the reaction is
N2H4 + 2H2O2 → N2 + 4H2O
The displayed formulae for the reactants and products are
The tables give the bond energies for the bonds broken in the reactants and the bonds made in the products.
| Bonds broken | Bonds made | ||
|---|---|---|---|
| bond | bond energy in kJ/mol | bond | bond energy in kJ/mol |
| N—N | 159 | NN | 945 |
| N—H | 391 | ||
| O—O | 143 | O—H | 463 |
| O—H | 463 |
i) Use the data in the tables to calculate the total amount of energy required to break all of the bonds in the reactants.
(1 mark)
energy required = .............................................................. kJ
ii) Use the data in the tables to calculate the total amount of energy released when all of the bonds in the products are made.
(1 mark)
energy released = .............................................................. kJ
iii) Calculate the enthalpy change, ∆H, in kJ/mol, for the reaction.
Include a sign in your answer.
(3 marks)
∆H = .............................................................. kJ/mol
Explain, in terms of bonds broken and bonds made, why this reaction is exothermic.
Draw an energy level diagram for the reaction between N2H4 and H2O2
Oxygen can be prepared from hydrogen peroxide using a catalyst.
Which is a correct statement about oxygen?
Choose your answer
it burns with a squeaky pop
it relights a glowing splint
it turns blue litmus red
it turns limewater milky
Explain how a catalyst increases the rate of a reaction.
The equation for the preparation of oxygen from hydrogen peroxide is
2H2O2 → 2H2O + O2
This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.
2H—O—O—H → 2H—O—H + O=O
The table gives the bond energies for these bonds.
i) Use the values in the table to calculate the enthalpy change, ΔH, for the reaction. Include a sign in your answer.
(3 marks)
ii) Complete the energy level diagram to show the position of the products and the enthalpy change, ΔH, for the reaction.
(2 marks)
Chlorine reacts with methane in sunlight.
CH4 + Cl2 → CH3Cl + HCl
The diagram below shows the displayed formulae for the reaction of chlorine with methane.
The table below shows the bond energies and the overall energy change in the reaction.
| C-H | Cl-Cl | C-Cl | H-Cl | Overall energy change | |
|---|---|---|---|---|---|
| Energy in kJ/mol | 413 | 243 | X | 432 | -122 |
What is the value of X?
Choose your answer
67
134
346
542
The reaction between hydrogen and chlorine is exothermic. This is the equation for the reaction.
H2 (g) + Cl2 (g) → 2HCl (g) ΔH = −184kJ
State the meaning of the term exothermic.
The table gives the bond energies for the H–H and H–Cl bonds.
| Bond | H–H | H–Cl |
|---|---|---|
| Bond energy in kJ/mol | 436 | 431 |
Use the equation and information from the table to calculate the bond energy of the Cl–Cl bond.
bond energy = .............................................................. kJ/mol
Explain why this reaction is exothermic. Refer to bond-breaking and bond-making in your answer.
Complete the reaction profile diagram to show the position of the products, the enthalpy change (ΔH) and the activation energy (Ea) for the reaction.
This question is about chemical energy changes.
Zinc reacts with copper(II) sulfate solution to form copper and zinc sulfate
A student uses this apparatus to measure the temperature change of the reaction.
This is the student’s method.
The diagram shows the thermometer readings before and after adding the zinc powder.
i) Complete the table, giving all values to the nearest 0.1o C.
| temperature in oC after adding the zinc | |
|---|---|
| temperature in oC before adding the zinc | 17.7 |
| temperature rise in °C |
(2 marks)
ii) Calculate the heat energy change in the reaction.
Give your answer to two significant figures.
[c = 4.2 J/g/oC]
(4 marks)
i) State two observations you might expect to see in the reaction
(2 marks)
ii) Give the name of the type of reaction taking place.
(1 mark)
A student investigates the reaction between hydrochloric acid and sodium hydroxide.
The equation for the reaction is:
HCl + NaOH → NaCl + H2O
This is her method.
i) State the type the reaction taking place between an acid and a base.
(1 mark)
ii) State a reason for using a polystyrene cup.
(1 mark)
iii) Suggest why the student used more hydrochloric acid than sodium hydroxide solution.
(1 mark)
The student recorded the following results:
| volume of sodium hydroxide solution in cm3 | 25.0 |
|---|---|
| initial temperature in oC | 18.0 |
| final temperature in oC | 24.2 |
i) Show that the heat energy change (Q) is about 1425 J.
[for the solution, c = 4.18 J/g/°C]
[mass of 1.00 cm3 of solution = 1.00 g]
(3 marks)
ii) Calculate the number of moles of sodium hydroxide reacted.
(1 mark)
iii) Calculate the value of the enthalpy change (ΔH), in kilojoules per mole, for the reaction between sodium hydroxide and hydrochloric acid.
Include a sign in your answer.
(3 marks)
When aqueous solutions of potassium hydroxide and nitric acid are mixed together, an exothermic reaction occurs. The diagram shows the apparatus used in an experiment to measure the temperature increase.
This is the student’s method:
A teacher advises the student to use a 50 cm3 burette instead of the 10 cm3 measuring cylinder. Suggest two reasons why it would be better to use a burette instead of a measuring cylinder to add the acid in this experiment.
The diagram shows the thermometer readings at the start and at the end of one experiment.
Complete the table to show:
| thermometer reading at end / °C | 26.8 |
|---|---|
| thermometer reading at start / °C | |
| thermometer rise / °C |
Another student uses the same method, adding the dilute nitric acid from a burette. The table shows his results.
This is the student’s graph.
The point where the lines cross represents complete neutralisation.
i) Identify the maximum temperature reached during the experiment.
(1 mark)
maximum temperature = .............................................................. °C
ii) Identify the volume of dilute nitric acid that exactly neutralises the 25 cm3 of aqueous potassium hydroxide.
(1 mark)
volume = .............................................................. cm3
Another student records these results.
| volume of aqueous potassium hydroxide | 20.0 cm3 |
|---|---|
| starting temperature of aqueous potassium hydroxide | 18.5 °C |
| maximum temperature of mixture | 30.0 °C |
| volume of dilute nitric acid | 20.0 cm3 |
Calculate the heat energy released in this experiment.
| c = 4.2 J /g/ °C |
|---|
| mass of 1 cm3 of mixture = 1 g |
heat energy = .............................................................. J
In another experiment, the heat energy released is 1600 J when 0.040 mol of potassium hydroxide is neutralised. Calculate the value of ΔH, in kJ/mol, for the neutralisation of potassium hydroxide.
ΔH = .............................................................. kJ/mol
A student investigates the reaction between magnesium and hydrochloric acid.
He uses this method:
Step 1: add 25 cm3 of dilute hydrochloric acid to a polystyrene cup
Step 2: record the temperature of the acid
Step 3: find the mass of a 10 cm strip of magnesium ribbon
Step 4: add the magnesium ribbon to the hydrochloric acid
Step 5: when all the magnesium has reacted, record the highest temperature reached
Complete the word equation for the reaction.
magnesium + hydrochloric acid → ......................... + ...........................
The thermometer shows the temperature of the acid at the start of the experiment.
i) Complete the table by giving the temperatures to the nearest 0.1 °C.
(2 marks)
| temperature of the acid at the start in °C | |
|---|---|
| highest temperature reached in °C | |
| temperature rise in °C | 20.8 |
ii) Show that the heat energy change (Q) for this reaction is about 2200 J.
[mass of 1.0 cm3 of solution = 1.0 g]
[for the solution, c = 4.2 J / g / °C]
(2 marks)
iii) The mass of magnesium used by the student was 0.12 g.
Calculate the value of the enthalpy change (ΔH), in kilojoules per mole of magnesium, for the reaction between magnesium and hydrochloric acid.
Include a sign in your answer.
(4 marks)
The reaction between magnesium and copper(II) sulfate solution is exothermic. This apparatus is used to measure the temperature increase when excess magnesium is added to 100 cm3 of copper(II) sulfate solution.
i) State why a reaction occurs when magnesium is added to copper(II) sulfate solution.
(1 mark)
ii) Complete the word equation for this reaction.
(1 mark)
magnesium + copper(II) sulfate .............................................................. + ..............................................................
The temperature at the start of the reaction is 20.2 °C. The maximum temperature recorded is 56.3 °C.
i) Calculate the heat energy change, in joules, for the reaction.
[mass of 1.00 cm3 of solution = 1.00 g] [c for the solution = 4.2 J/g/ °C]
(2 marks)
heat energy change = .............................................................. J
ii) Explain why it is better to use a polystyrene cup rather than a glass beaker in this experiment.
(2 marks)
The reaction between zinc and copper(II) sulfate solution is also exothermic.
i) A mass of 0.500 g of zinc is reacted with an excess of copper(II) sulfate solution. The heat energy change is 1.67 kJ. Calculate the molar enthalpy change, ΔH, in kJ/mol. Include a sign in your answer. Give your answer to three significant figures.
(3 marks)
ΔH = .............................................................. kJ/mol
ii) The ionic equation for the reaction between zinc and copper(II) sulfate is
Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)
Explain why this is a redox reaction.
(3 marks)
A student uses this apparatus to investigate the reaction between potassium hydroxide solution and dilute hydrochloric acid.
This is her method.
i) Give a word equation for the reaction between potassium hydroxide and hydrochloric acid.
(1 mark)
ii) Explain why the student needs to stir the mixture.
(2 marks)
The table gives the temperatures of the solutions before the student mixes them.
| potassium hydroxide solution | 17.8 °C |
|---|---|
| dilute hydrochloric acid | 18.4 °C |
Calculate the mean (average) temperature of the two solutions.
mean temperature = .............................................................. °C
The student repeats the experiment on a different day, using 25 cm3 of potassium hydroxide solution and 25 cm3 of dilute hydrochloric acid. The thermometer shows the highest temperature reached at the end of the experiment.
i) Complete the table by giving the missing information.
Give both temperatures to the nearest 0.1 oC.
| Mean temperature at start in °C | |
|---|---|
| Temperature at end in °C | |
| Temperature rise in °C | 5.2 |
(2 marks)
ii) Show that the heat energy change, Q, in the student’s experiment is about 1100J.
[for the mixture, c = 4.2 J / g / °C]
[mass of 1.0cm3 of mixture = 1.0g]
(3 marks)
iii) The student uses 0.020mol of potassium hydroxide in his experiment.
Calculate the enthalpy change (ΔH) in kJ/mol, for 1.0 mol of potassium hydroxide.
Include a sign in your answer.
(3 marks)
A student investigates the temperature change during the reaction between zinc metal and copper(II) sulfate solution.
The student considers two different methods.
Method 1
Method 2
Discuss the advantages and disadvantages of each method.
The equation for the reaction is
Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
50cm3 of copper(II) sulfate solution contains 0.025 mol CuSO4
A mass of 3 g of zinc is used.
Show that the zinc is in excess.
[Ar of zinc = 65]
The student reacts a solution containing 0.025 mol CuSO4 with an excess of zinc.
These are the student’s results.
i) Show that the energy change Q for this reaction is about 4000 J
[mass of 1 cm3 of solution = 1.0 g]
[for the solution, c = 4.2 J / g / °C]
(3 marks)
ii) Calculate the molar enthalpy change (ΔH), in kJ / mol, for the reaction.
(3 marks)
ΔH = .............................. kJ / mol
The ionic equation for the reaction is
Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)
Explain what is oxidised and what is reduced in this reaction.
How much energy is needed to break all the bonds in 0.025 g of nitrogen gas?
The relative atomic mass, Ar, of N is 14.
| Bond | Bond energy in kJ/mol |
|---|---|
| NN | 945 |
Choose your answer
1701 J
1701 kJ
844 J
844 kJ
A car manufacturer claims a car model consumes 56 miles per gallon of petrol (gasoline).
When a kilogram of gasoline is burned, 5.3 x 105 kJ of heat energy is produced.
(1 gallon = 4.54 litres)
i) Calculate how many miles per litre the car consumes.
(1 mark)
ii) Calculate the heat energy change, in kJ/mol, produced by the fuel.
You should assume the gasoline is pure octane, C8H18.
Give your answer to three significant figures.
(Mr* *of C8H18 = 114 )
(3 marks)
iii) The manufacturer claims the car can travel 650 miles on a full tank of petrol. Deduce the size of the fuel tank in litres.
(1 mark)
When the fuel burns, the carbon in the octane turns into carbon dioxide:
2C8H18 + 25O2 → 16CO2 + 18H2O
Calculate the volume of carbon dioxide gas at room temperature and pressure when 1.0 kg of the fuel burns.
[for a gas, molar volume = 24 dm3 at rtp]
The data in the table gives some information and bond energies.
| Bond | Bond energy in kJ/mol |
|---|---|
| C-H | 413 |
| O=O | 498 |
| C=O | 805 |
| H-O | 464 |
Use the information to calculate the enthalpy of reaction for the combustion of carbon:
CH4 + 2O2 CO2 + 2H2O
Draw a reaction profile to represent the combustion of carbon, including labels for activation energy and the enthalpy change:
