(a)(i) Explain what is meant by acid anhydride and give one example
(ii) State three chemical properties of hydrochloric acid.
(b) Explain each of the following observations:
(i) Tetraoxosulphate (VI) acid can form two types of salts unlike trioxonitrate (V) acid.
(ii) Copper and iron react with concentrated H\(_2\)SO\(_4\) but only one of them reacts with the dilute acid.
(iii) On adding dilute H\(_2\)SO\(_4\) separately to zinc dust and zinc granules of the same mass, the dust produced more vigorous effervescence.
(c)(i) Define activation energy.
(ii) Sketch and label an energy profile diagram for the following reaction: A + B –> C + D; AH = xkJmol\(^{-1}\)
(iii) Explain why the heat of reaction of the mineral acids with sodium hydroxide is constant in value.
(d) Consider the reaction represented by the following equation:
Q\(_{(s)}\) \(\rightleftharpoons\) Q\(_{(l)}\) \(\Delta\) = xkJmol\(^{-1}\)
(i) State with reason which of Q\(_{(s)}\) and O\(_{(J)}\) has the higher entropy.
(ii) What will be the effect of decrease in temperature on the system at equilibrium?
Explanation
(a)(i) Acid anhydride means acid without water. e.g. SO\(_2\), CO\(_2\), etc.
(ii) HCI react with metals more electropositive than hydrogen to liberate hydrogen gas.
-HCI reacts with bases or alkali to produce salt and water only.
-They react with trioxocarbonate (IV) and hydrogen trioxocarbonate (IV) to literate carbon (IV) oxide.
(b)(i) H\(_2\)SO\(_4\) can form a neutral salt and also an acid salt while NHO\(_3\) can only form a neutral salt.
(ii) Both copper and iron have low standard electrode potential and only iron reacts with the dilute acid because it is more active than copper
(iii) The zinc dust has larger area of contact for the reaction to take place unlike the zinc granules.
(c)(i) Activation energy in the combined energy which the reactant particles must have in order to react or for a reaction to occur.
(iii) The heat of reaction of the mineral acids with sodium hydroxide is constant because the only change that actually occurs during the reaction is the formation of water molecule which has an approximately constant value of- 57.4 kJmol\(^{-1}\)
(d)(i) Q\(_{(s)}\) has higher entrophy because the molecules of Q\(_{(s)}\) are free to move than that of Q\(_{(s)}\)
(ii) Decrease in temperature will favour the reverse reaction.