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 |
| ☐ | A | ||
| ☐ | B | ||
| ☐ | C | ||
| ☐ | D |
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Which statement is true about exothermic and endothermic reactions?
| ☐ | A | The products have more energy than the reactants in an exothermic reaction | |
| ☐ | B | The products have more energy than the reactants in an endothermic reaction | |
| ☐ | C | The activation energy for an exothermic reaction is always larger than the activation energy for an endothermic reaction | |
| ☐ | D | Most reactions are endothermic |
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1 markWhen solid sodium oxide is added to water, an exothermic reaction occurs:
Na2O (s) + H2O (l)format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math12bba9f4124283edd644799e0ce%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%2210.5%22%20y%3D%2216%22%3E%26%23x2192%3B%3C%2Ftext%3E%3C%2Fsvg%3E)
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
| ☐ | A | Q = 2,310 J | |
| ☐ | B | Q = 2,450 J | |
| ☐ | C | Q = 139 J | |
| ☐ | D | Q = 126 J |
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The graph below shows a reaction profile for the reaction between methane and oxygen.
What does the label X represent?
| ☐ | A | Activation Energy | |
| ☐ | B | Overall energy change | |
| ☐ | C | Reactants | |
| ☐ | D | Progress of the reaction |
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1 markThe reaction profile for making nitrogen monoxide, NO, is shown below:
What is the activation energy for this reaction?
| ☐ | A | +140 kJ | |
| ☐ | B | +180 kJ | |
| ☐ | C | +320 kJ | |
| ☐ | D | -330 kJ |
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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.
2 marksThe 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.
Identify the volume of dilute nitric acid that exactly neutralises the 25 cm3 of aqueous potassium hydroxide.
(1)
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 |
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.
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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.
8 marksThe thermometer shows the temperature of the acid at the start of the experiment.
| temperature of the acid at the start in °C | |
| highest temperature reached in °C | |
| temperature rise in °C | 20.8 |
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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.
(1)
(1)
magnesium + copper(II) sulfate .............................................................. + ..............................................................
The temperature at the start of the reaction is 20.2 °C.
The maximum temperature recorded is 56.3 °C.
[mass of 1.00 cm3 of solution = 1.00 g] [c for the solution = 4.2 J/g/ °C]
(2)
heat energy change = .............................................................. J
(2)
The reaction between zinc and copper(II) sulfate solution is also exothermic.
(3)
ΔH = .............................................................. kJ/mol
Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)
Explain why this is a redox reaction.
(3)
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A student uses this apparatus to investigate the reaction between potassium hydroxide solution and dilute hydrochloric acid.
This is her method.
2 marksThe 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
8 marksThe 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.
| Mean temperature at start in °C | |
| Temperature at end in °C | |
| Temperature rise in °C | 5.2 |
(3)
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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
2 marksThe equation for the reaction is
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]
6 marksThe student reacts a solution containing 0.025 mol CuSO4 with an excess of zinc.
These are the student’s results.
The ionic equation for the reaction is
Explain what is oxidised and what is reduced in this reaction.
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1 markHow 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 |
Nformat('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math197ea3cfb64eeaa1edba65501d0%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%228.5%22%20y%3D%2216%22%3E%26%23x2261%3B%3C%2Ftext%3E%3C%2Fsvg%3E) N |
945 |
| ☐ | A | 1701 J | |
| ☐ | B | 1701 kJ | |
| ☐ | C | 844 J | |
| ☐ | D | 844 kJ |
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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.
3 marksThe 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 |
6 marksIn 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.
2 marksAnother 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.
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2 marksA 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 in oC | 20.0 |
| Lowest temperature of solution in oC | 14.2 |
Use the results of the experiment to explain what type of reaction is taking place when ammonium nitrate is added to water.
3 marksShow 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]
4 marksUse 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.
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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?
| ☐ | A | Electronic balance, measuring cylinder, glass beaker, thermometer | |
| ☐ | B | Measuring cylinder, glass beaker, polystyrene cup, thermometer | |
| ☐ | C | Electronic balance, glass beaker, polystyrene cup, thermometer | |
| ☐ | D | Measuring cylinder, glass beaker, glass rod, thermometer |
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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.
(1)
(2)
6 marks(3)
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 |
(2)
(2)
ΔH = ...................................................................... kJ/mol
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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
10 marksLithium 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.
(2)
| temperature in °C after adding the lithium oxide | |
| temperature in °C before adding the lithium oxide | 17.3 |
| temperature rise in °C |
(4)
heat energy change = .............................. J
| amount of lithium oxide in mol | 0.0580 |
| heat energy change in J | 5210 |
(3)
ΔH = ..............................kJ / mol
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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.
(1)
(2)
7 marksThe 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 |
(3)
(1)
(3)
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5 marksDuring 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
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 | N=N | 945 | |
| N—H | 391 | |||
| O—O | 143 | O—H | 463 | |
| O—H | 463 | |||
(1)
energy required = .............................................................. kJ
(1)
energy released = .............................................................. kJ
Include a sign in your answer.
(3)
∆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
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Oxygen can be prepared from hydrogen peroxide using a catalyst.
Which is a correct statement about oxygen?
| ☐ | A | it burns with a squeaky pop |
| ☐ | B | it relights a glowing splint |
| ☐ | C | it turns blue litmus red |
| ☐ | D | it turns limewater milky |
5 marksThe equation for the preparation of oxygen from hydrogen peroxide is
This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.
The table gives the bond energies for these bonds.
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1 markChlorine 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?
| ☐ | A | 67 | |
| ☐ | B | 134 | |
| ☐ | C | 346 | |
| ☐ | D | 542 |
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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.
4 marksThe 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.
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