Topic 5 Chem Energetics Questions

This question is about an experiment to measure the enthalpy of combustion, ΔH_c, of ethanol, using the apparatus and setup shown. Which quantity is likely to be the most inaccurate due to the sources of error in this experiment?

• Mass of ethanol burnt

• Molecular mass of ethanol

• Mass of water

• Temperature change

When equal masses of X and Y absorb the same amount of energy, their temperatures rise by 5 °C and 10 °C respectively. Which is correct?

• The specific heat capacity of X is twice that of Y.

• The specific heat capacity of X is half that of Y.

• The specific heat capacity of X is one fifth that of Y.

• The specific heat capacity of X is the same as Y.

Which is correct when Ba(OH)₂ reacts with NH₄Cl?

• A

• B

• C

• D

The enthalpy of combustion of ethanol is determined by heating a known mass of tap water in a glass beaker with a flame of burning ethanol. Which will lead to the greatest error in the final result?

• Assuming the density of tap water is 1.0 g cm⁻³

• Assuming all the energy from the combustion will heat the water.

• Assuming the specific heat capacity of the tap water is 4.18 J g⁻¹ K⁻¹

• Assuming the specific heat capacity of the beaker is negligible

Two 100 cm³ aqueous solutions, one containing 0.010 mol NaOH and the other 0.010 mol HCl, are at the same temperature.

When the two solutions are mixed the temperature rises by y °C.

Assume the density of the final solution is 1.00 g cm⁻³.

Specific heat capacity of water = 4.18 J g⁻¹ K⁻¹

What is the enthalpy change of neutralization in kJ mol⁻¹?

• A

• B

• C

• D

Which statement is correct for this reaction?

Fe₂O₃ (s) + 3CO (g) → 2Fe (s) + 3CO₂ (g) ΔH = −26.6 kJ

• 13.3 kJ are released for every mole of Fe produced.

• 26.6 kJ are absorbed for every mole of Fe produced.

• 53.2 kJ are released for every mole of Fe produced.

• 26.6 kJ are released for every mole of Fe produced.

Which expression gives the mass, in g, of ethanol (C₂H₆O)required to produce 683.5 kJ of heat upon complete combustion?

(M_r for ethanol = 46.0, ΔH^θ_c=−1367 kJmol⁻¹)

• A

• B

• C

• D

The combustion of glucose is exothermic and occurs according to the following equation:

C₆H₁₂O₆ (s) + 6O₂ (g) → 6CO₂ (g) + 6H₂O (g)

Which is correct for this reaction?

• A

• B

• C

• D

The enthalpy change for the dissolution of NH₄NO₃ is +26 kJ mol^–1 at 25 °C. Which statement about this reaction is correct?

• The reaction is exothermic and the solubility decreases at higher temperature.

• The reaction is exothermic and the solubility increases at higher temperature.

• The reaction is endothermic and the solubility decreases at higher temperature.

• The reaction is endothermic and the solubility increases at higher temperature.

Which change of state is exothermic?

• CO₂(s) → CO₂(g)

• H₂O(l) → H₂O(g)

• NH₃(g) → NH₃(l)

• Fe(s) → Fe(l)