Energetics (Triple) quiz

1. Is making new bonds exothermic or endothermic?

Depends on the reagents

Endothermic

Depends on the temperature of the surroundings

Exothermic

Question 1 of 16

2. Are combustion reactions exothermic or endothermic?

Depends on the temperature of the surroundings

Exothermic

Depends on the reagents

Endothermic

Question 2 of 16

3. What does the symbol ΔH mean

heat energy

exothermic

enthalpy (energy) change

specific heat capacity

Question 3 of 16

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

-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)

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

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

Question 4 of 16

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

Endothermic

Depends on the reagents

Exothermic

Depends on the temperature of the surroundings

Question 5 of 16

6. Are neutralisation reactions exothermic or endothermic?

Endothermic

Exothermic

Depends on the temperature of the surroundings

Depends on the reagents

Question 6 of 16

7. State the units of molar enthalpy change.

kJ/mol

mol/⁰C

kJ/⁰C

J/⁰C/mol

Question 7 of 16

8. What does this diagram represent?

Energy level diagram for an endothermic reaction

Reaction profile for an endothermic reaction

Energy level diagram for an exothermic reaction

Reaction profile for an exothermic reaction

Question 8 of 16

9. 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

1944 J

355 kJ/mol

355 J

Question 9 of 16

10. What is meant by the term endothermic?

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

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

Question 10 of 16

11. What is meant by the term exothermic?

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

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

Question 11 of 16

12. 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 12 of 16

13. 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

Energy taken in when making bonds

Depends on the temperature of the surroundings

Energy taken in when breaking bonds

Question 13 of 16

14. 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 ensure the container does not get too hot

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

To prevent the water from evaporating

Question 14 of 16

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

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

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

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

Question 15 of 16

16. Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?

2.153 kJ

2153 J

1254 J

3383 J

Question 16 of 16

Energetics (Triple) quiz

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