Rate of Reaction

1. When powdered calcium carbonate is added to a solution of hydrochloric acid, it reacts completely within seconds. When the same mass of calcium carbonate chips is used, the reaction takes several minutes. Why?

• An acid will react faster with a powder

• There are more impurities in the calcium carbonate chips

• The powder has a greater surface areas

• The calcium carbonate chips are less soluble than the powder

Which one of the following reactants is most likely to have the slowest rate of reaction?

• A covalent compound in solution and an ionic substance in solution

• Two ionic substances in solution

• Two solid ionic substances

• Two covalent compounds in solution

Magnesium ribbon is reacted with dilute hydrochloric acid. Which one of the following graphs best describes the relationship between the rate of reaction and time as the reaction proceeds?

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Answer explanation

The rate will will start fast when the concentration of the acid is high, but as the acid is used up, its concentration decreases, collisions between the magnesium and the acid become less frequent, and the rate reduces.

Which two of the following would make the most suitable catalysts in the decomposition of hydrogen peroxide (H₂O₂)?

• Sodium chloride (NaCl)

• Manganese dioxide (MnO₂)

• Manganese oxide (MnO)

• Liver

Answer explanation

Both manganese dioxide and liver are good catalysts for this decomposition. You just need to remember that it is managanese dioxide and not manganese oxide. Sorry!

In a reaction between two gases, which one of the following factors will not affect the rate of reaction?

• Pressure

• Temperature

• Colour

• Volume of the container the gases are in.

If the temperature of a reaction is decreased, what effect will this have on the rate of reaction?

• The reaction will stop

• The rate of reaction will increase

• It will have no effect

• The rate of reaction will decrease

Catalysts are used in industry because

• they remove the products from the reaction mixture as the products form

• they increase the rate at which the products are formed

• they increase the yield of the products

• they lower the temperature at which the reaction can proceed

What effect does doubling the concentration of one of the reactants have on the rate of reaction?

• The rate of reaction is halved

• It has no effect

• It increases the rate of reaction

• It decreases the rate of reaction

A catalyst

• will have a change in its mass at the end of a chemical reaction

• must be in the same phase (state of matter) as the reactants

• will always react with the reactants in a chemical reaction

• will be chemically unchanged at the end of a reaction

Which one of the following equations best describes an experiment to monitor the decomposition of hydrogen peroxide using a catalyst? (The writing in the middle of the arrow, in the square brackets, is normally written over the arrow.)

• 2H₂O₂ -----[MnO₄^-]-----> H₂O + O₂

• H₂O + 1/2 O₂ -------[catalyst]-------> H₂O₂

• H₂O₂ ------[MnO₂]-----> H₂O + 1/2 O₂

• H₂O₂ -------[heat]-----> H₂O + 1/2 O₂

Answer explanation

Make sure the hydrogen peroxide is on the left, the equation is balanced, and a catalyst is used!