(a) (i) State the collision theory of reaction rates. (ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical rea...
(a) (i) State the collision theory of reaction rates.
(ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.
(b) (i) Sketch a graphical representation of Charles’ law.
(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol at s.t.p.
[molar volume at s.t.p = \(22.4\ \text{dm}^3\)]
(c) (i) Define esterification.
(ii) Give two uses of alkanoates.
(iii) Give the products of the alkaline hydrolysis of ethyl ethanoate.
(d) A tin coated plate and a galvanized plate were exposed for the same length of time.
(i) Which of the two plates corrodes faster?
(ii) Explain briefly your answer in 2 (d) (i).
(a) (i) The collision theory states that reactant particles must collide before a reaction can occur. Only collisions with sufficient energy to overcome the activation energy, and with the correct orientation where necessary, result in reaction.
(a) (ii) When the temperature is increased, the reactant particles gain kinetic energy and move faster. Collisions occur more frequently, and a greater proportion of the collisions have energy equal to or greater than the activation energy. Therefore, the number of effective collisions per second increases and the reaction rate increases.
(b) (i) At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature in kelvin. Hence, a graph of volume against temperature in kelvin is a straight line passing through the origin.
Graph of volume against absolute temperature (kelvin): a straight line through the origin.
(b) (ii)
The balanced equation for the complete combustion of ethanol is:
From the equation, 1 mole of ethanol requires 3 moles of oxygen.
\[\text{Moles of }O_2 = 2.5 \times 3 = 7.5\text{ mol}\]
\[\text{Volume of }O_2 = 7.5 \times 22.4 = 168.0\text{ dm}^3\]
Therefore, the volume of oxygen required is 168.0 dm3 at s.t.p.
(c) (i) Esterification is the reaction between an alkanol and an alkanoic acid, usually in the presence of concentrated sulfuric acid, to form an ester and water.
(c) (ii) Uses of alkanoates include:
as solvents, for example in paints, varnishes and nail polish removers;
in perfumes and artificial food flavourings.
(c) (iii) Alkaline hydrolysis of ethyl ethanoate produces ethanol and an ethanoate salt.
(d) (ii) Zinc is more reactive than iron and acts as a sacrificial metal in a galvanized plate. Zinc corrodes preferentially and protects the iron plate. Tin is less reactive than iron; therefore, when the tin coating is damaged or exposed, the iron corrodes readily in contact with tin.
(a) (i) The collision theory states that reactant particles must collide before a reaction can occur. Only collisions with sufficient energy to overcome the activation energy, and with the correct orientation where necessary, result in reaction.
(a) (ii) When the temperature is increased, the reactant particles gain kinetic energy and move faster. Collisions occur more frequently, and a greater proportion of the collisions have energy equal to or greater than the activation energy. Therefore, the number of effective collisions per second increases and the reaction rate increases.
(b) (i) At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature in kelvin. Hence, a graph of volume against temperature in kelvin is a straight line passing through the origin.
Graph of volume against absolute temperature (kelvin): a straight line through the origin.
(b) (ii)
The balanced equation for the complete combustion of ethanol is:
From the equation, 1 mole of ethanol requires 3 moles of oxygen.
\[\text{Moles of }O_2 = 2.5 \times 3 = 7.5\text{ mol}\]
\[\text{Volume of }O_2 = 7.5 \times 22.4 = 168.0\text{ dm}^3\]
Therefore, the volume of oxygen required is 168.0 dm3 at s.t.p.
(c) (i) Esterification is the reaction between an alkanol and an alkanoic acid, usually in the presence of concentrated sulfuric acid, to form an ester and water.
(c) (ii) Uses of alkanoates include:
as solvents, for example in paints, varnishes and nail polish removers;
in perfumes and artificial food flavourings.
(c) (iii) Alkaline hydrolysis of ethyl ethanoate produces ethanol and an ethanoate salt.
(d) (ii) Zinc is more reactive than iron and acts as a sacrificial metal in a galvanized plate. Zinc corrodes preferentially and protects the iron plate. Tin is less reactive than iron; therefore, when the tin coating is damaged or exposed, the iron corrodes readily in contact with tin.
