Enthalpy Change, ΔH (CIE A Level Chemistry)

A student mixed 30.0 cm³ of 0.0250 mol dm^-3 potassium hydroxide solution with 30.0 cm³ of 0.0250 mol dm^-3 nitric acid. The temperature rose by 0.50 ^oC. Assume no heat was lost to the surroundings. 

The final mixture had a specific heat capacity of 4.18 J cm^-3 K^-1.

What is the molar enthalpy change for the reaction?

An experiment was carried out to determine the approximate value for the molar enthalpy change of neutralisation. 

75 cm³ of 3.00 mol dm^–3 hydrochloric acid was placed in a polystyrene beaker of negligible heat capacity. Its temperature was recorded, and then 75 cm³ of 3.00 mol dm⁻³ potassium hydroxide at the same temperature was quickly added, and the solution was stirred. 

The temperature rose by 14 °C. The resulting solution may be considered to have a specific heat capacity of 4.18 J g^-1 K^-1.

Calculate the molar enthalpy change of neutralisation.

The standard enthalpy change ∆H^θ for the below reaction is -1776 kJ.

2N (g) + 6F (g) → 2NF₃ (g)

What is the bond energy of the N–F bond?

The complete combustion of ethyne, C₂H₂, is shown in the equation below.

H−C≡C−H + 2½ O=O → O−H−H + 2O=C=O

Using the average bond enthalpies given in the table, what is the enthalpy change of combustion of ethyne?

Compound R into compound T, it was found that the reaction proceeded by way of compound S, which could be isolated. The following steps were involved.

R → S;   ΔH is positive

S → T;   ΔH is negative

Which reaction profile fits these data?

The table below discusses three types of enthalpy change:

   ‘+’ means that this type of standard enthalpy change can only have positive values.

   ‘–’ means that this type of standard enthalpy change can only have negative values.

   ‘+ / –’ means that either positive or negative values are possible.

Which row is correct?

In the gas phase, phosphorus pentachloride can be thermally decomposed into gaseous phosphorus trichloride and chlorine. 

PCl₅ → PCl₃ + Cl₂

The table below gives the relevant bond energies found in these compounds.

What is the enthalpy change in the decomposition of the reaction?

In a calorimetric experiment 2.50 g of a fuel is burnt in oxygen. 30 % of the energy released during the combustion is absorbed by 500 g of water, the temperature of which rises from 25 °C to 68 °C. 

The specific heat capacity of water is 4.18 J g^–1 K^–1.

What is the total energy released per gram of fuel burnt?

Which equation correctly shows how the bond energy for the covalent bond Y-Z can be calculated by dividing ΔH by n?

The diagram shows the skeletal formula of cyclobutane.

The enthalpy change of formation of cyclobutane is +75.1 kJ mol^–1, and the enthalpy change of atomisation of graphite is +712 kJ mol^–1.

The bond enthalpy of C–H is 390 kJ mol^–1 and of H–H is 429 kJ mol^–1.

What is the average bond enthalpy of the C–C bond in cyclobutane, rounded to the nearest whole number?

Some bond energy values are listed below.

These bond energy values relate to the following four reactions:

What is the correct order of enthalpy changes of the above reactions from most negative to most positive?