Nitrogen and sulfur — Chemistry 9701 AS & A Level Question & Worked Solution

(a)[3]

State what is meant by the standard enthalpy change of formation, $\Delta H_f^{\circ}$.

(b(i))

Hydrazine reacts with oxygen in the equation $\text{N}_2\text{H}_4(l) + \text{O}_2(g) \rightarrow \text{N}_2(g) + 2\text{H}_2\text{O}(g)$. Use the table data to work out the standard enthalpy change for this reaction.

(b(ii))

Although the reaction above is highly exothermic, hydrazine does not ignite spontaneously in oxygen. Suggest a reason for this.

(b(iii))[4]

Suggest why using hydrazine as a rocket fuel could be considered environmentally friendly.

(c(i))

The bonding in hydrazine is similar to the bonding in ammonia. Using only outer-shell electrons, draw a dot-and-cross diagram of an ammonia molecule.

(c(ii))

Draw a diagram to represent the three-dimensional shape of an ammonia molecule.

(c(iii))[4]

Draw a diagram to show the shape of a hydrazine molecule. Show clearly which atom is attached to which, and also show the value of one bond angle clearly.

(d)[1]

Deduce the oxidation state of nitrogen in the hydrazine molecule.

Nitrogen and sulfur — practice question

Worked solution & mark scheme