Energetics (Triple) quiz

1. Explain, in terms of making and breaking bonds, why a reaction could be exothermic

The energy needed to break the bonds is less than the energy released to make the bonds

Breaking the bonds is less favourable than making them

The bonds in the reagents are stronger than the bonds in the products

The energy needed to break the bonds is more than the energy released to make the bonds

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 ensure the container does not get too hot

To prevent the water from evaporating

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

Question 2 of 16

3. In a chemical reaction, 250 kJ/mol is taken to break all the bonds and 280 kJ/mol is released when new bonds are formed. What is the overall molar enthalpy of the reaction?

+530 kJ/mol

-30 kJ/mol

-530 kJ/mol

+30 kJ/mol

Question 3 of 16

4. State the units of molar enthalpy change.

mol/⁰C

kJ/mol

kJ/⁰C

J/⁰C/mol

Question 4 of 16

5. What is meant by the term endothermic?

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

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

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 5 of 16

6. 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

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

Question 6 of 16

7. 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 7 of 16

8. Are displacement reactions exothermic or endothermic?

Depends on the temperature of the surroundings

Endothermic

Exothermic

Depends on the reagents

Question 8 of 16

9. Is breaking bonds exothermic or endothermic?

Depends on the temperature of the surroundings

Endothermic

Depends on the reagents

Exothermic

Question 9 of 16

10. What does the symbol ΔH mean

enthalpy (energy) change

specific heat capacity

exothermic

heat energy

Question 10 of 16

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

Depends on the reagents

Depends on the temperature of the surroundings

Endothermic

Exothermic

Question 11 of 16

12. 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?

1944 kJ

2.153 kJ

1170 J

1247 J

Question 12 of 16

13. 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?

3383 J

1254 J

2.153 kJ

2153 J

Question 13 of 16

14. What is meant by the term exothermic?

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

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

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 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. Are neutralisation reactions exothermic or endothermic?

Endothermic

Exothermic

Depends on the reagents

Depends on the temperature of the surroundings

Question 16 of 16

Energetics (Triple) quiz

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