Energetics (Triple) quiz

1. Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?

1944 kJ

355 J

355 kJ/mol

1944 J

Question 1 of 16

2. In a calorimetry experiment to investigate the heat energy released by the combustion of ethanol, why should the water in the calorimeter be stirred?

To allow the heat to spread evenly through the copper container

To prevent the water from evaporating

To ensure the container does not get too hot

To ensure the heat energy is mixed evenly throughout all the water

Question 2 of 16

3. State the units of molar enthalpy change.

J/⁰C/mol

mol/⁰C

kJ/mol

kJ/⁰C

Question 3 of 16

4. When a solid dissolves, is this process exothermic or endothermic?

Endothermic

Exothermic

Depends on the temperature of the surroundings

Depends on the reagents

Question 4 of 16

5. What is meant by the term exothermic?

A reaction which will only be spontaneous at warm temperatures (above 100⁰C)

A reaction in which heat energy is taken in (surroundings get colder)

A reaction which will only be spontaneous at cold temperatures (below 0⁰C)

A reaction in which heat energy is given out (surroundings get hotter)

Question 5 of 16

6. In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.

-738 kJ/mol (Amount = 0.78/46 = 0.017 mol. Answer = 12540/1000/0.017 = 738 kJ/mol)

-425 kJ/mol (Amount = 23/0.78 = 29.5 mol. Answer = 12540/29.5 = 425 kJ/mol)

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 kJ/mol)

-213 kJ/mol (Amount = 46/0.78 = 59.0 mol. Answer = 12540/59.0 = 213 kJ/mol)

Question 6 of 16

7. Is making new bonds exothermic or endothermic?

Endothermic

Exothermic

Depends on the reagents

Depends on the temperature of the surroundings

Question 7 of 16

8. Explain why experimental values of enthalpy change differ from theoretical values

Different equipment produces different results. Not all the reactants are used up

Different equipment produces different results. Heat energy is lost to the surroundings. Not all the reactants are used up

Heat energy is lost to the surroundings. Not all the reactants are used up.

Different equipment produces different results. Heat energy is lost to the surroundings

Question 8 of 16

9. Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?

1247 J

1944 kJ

1170 J

2.153 kJ

Question 9 of 16

10. In a chemical reaction, the overall molar enthalpy is +87 kJ/mol. Is this reaction exothermic or endothermic?

Depends on the reagents

Exothermic

Endothermic

Depends on the temperature of the surroundings

Question 10 of 16

11. What does this diagram represent?

Reaction profile for an endothermic reaction

Reaction profile for an exothermic reaction

Energy level diagram for an endothermic reaction

Energy level diagram for an exothermic reaction

Question 11 of 16

12. In an exothermic reaction, which is greater: the energy taken in when breaking bonds or the energy released when bonds are made?

Energy released when bonds are made

Depends on the temperature of the surroundings

Energy taken in when breaking bonds

Energy taken in when making bonds

Question 12 of 16

13. Assuming bond energies in kJ/mol: H-C 412, C-C 348, O-H 463, C-O 360, C=C 612. Calculate the molar enthalpy change for the reaction: ethanol → ethene + water

+45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Breaking - making = 3231-3186 = +45 kJ/mol)

-45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Making - breaking = 3186-3231 = -45 kJ/mol)

+96 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Breaking - making = 1583-1487 = +96 kJ/mol)

-45 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Making - breaking = 1487-1583 = -96 kJ/mol)

Question 13 of 16

14. Are neutralisation reactions exothermic or endothermic?

Exothermic

Depends on the reagents

Endothermic

Depends on the temperature of the surroundings

Question 14 of 16

15. What does this diagram represent?

Reaction profile for an endothermic reaction

Reaction profile for an exothermic reaction

Energy level diagram for an endothermic reaction

Energy level diagram for an exothermic reaction

Question 15 of 16

16. What is meant by the term endothermic?

A reaction in which heat energy is taken in (surroundings get colder)

A reaction in which heat energy is given out (surroundings get hotter)

A reaction which will only be spontaneous at warm temperatures (above 100⁰C)

A reaction which will only be spontaneous at cold temperatures (below 0⁰C)

Question 16 of 16

Energetics (Triple) quiz

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