1. The reaction between calcium carbonate and hydrochloric acid, carried out in an open flask, can be represented by the following equation:
CaCO2(s) + 2HCl(aq) ----------> CaCl2(aq) + H2O(l) + CO2(g)
Which of the measurements below could be used to measure the rate of reaction?
I The mass of the flask and contents
II The pH of the reaction mixture
III The volume of carbon dioxide produced
Answer: I, II, III
The pH of the reaction mixture could be used to measure the rate of reaction because the mixture will go from acidic to neutral, and the rate at which this happens can be measured.
2. For a given reaction, why does the rate of reaction increase when the concentration of the reactants are increased?
The frequency of the molecular collisions increases.
3. Based on the definition for the rate of reaction, which units are used for a rate?
mol dm-3 time -1
4. Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass of the beaker and contents was plotted against time (line 1)
What change in the experiment could give line 2?
I The same mass of magnesium but in smaller pieces
II The same volume of a more concentrated solution of hydrochloric acid
III A lower temperature
Answer: II only
5. The rate of a reaction between two gases increases when the temperature is increased and a catalyst is added. Which statements are both correct for the effect of these change son the reaction?
Increasing the temperature - Activation energy doesn't change
Adding a catalyst - Activation energy decreases
6. Consider the reaction between solid CaCO3 and aqueous HCl. The reaction will be speeded up by an increase in which of the following conditions?
I Concentration of HCl
II Size of the CaCO3 particles
III Temperature
Answer: I and III only
An increase in the size of the CaCO3 particles will slow down the reaction as there will be a smaller surface area of one of the reactants.
7. Which of the following is important in determining whether a reaction occurs.
I Energy of the molecules
II Orientation of the molecules
Answer: Both I and II
11. When excess lumps of magnesium carbonate are added to dilute hydrochloric acid the following reaction takes place:
MgCO3(s) + 2HCl(aq) ----------> MgCl2(aq) + CO2(g) + H2)(l)
(a) Outline two ways in which the rate of this reaction could be studied.
The volume of carbon dioxide produced could be measured consistently per unit of time by using a gas syringe or an inverted measuring cylinder filled with water. A stop clock would be used to keep track of the time.
The change of mass of the reactants could be measured consistently per unite of time as the reactions carries out by placing the reactants in a conical flask on a top pan balance. A stop clock is used to record the time.
(b) State and explain three ways in which the rate of reaction could be increased.
Increasing the temperature increases the frequency of collisions and the energy of the reacting molecules.
Increasing the concentration of HCl will increase the frequency of collisions as there would be more reactant HCl particles.
Using small pieces of solid magnesium carbonate will increase the surface area and result in an increase in the frequency of collisions as reacting particles will have more area to collide with each other.
(c) State and explain whether the total volume of carbon dioxide produced would increase, decrease or stay the same if:
(i) More lumps of magnesium carbonate were used.
The volume of carbon dioxide would stay the same as the same volume of HCl is used and it acts as a limiting factor.
(ii) The experiments were carried out at a higher temperature.
The volume of carbon dioxide would stay the same as the amount of reactants are used.
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