CHAPTER 3. REACTION RATES 3.5
- Now add the copperpieces to the same testtube. What happens tothe
rate at which the gas is produced? - Carefully remove thecopper pieces from thetest tube (do not get HCl on
your hands), rinse themin water and alcohol and then weigh them again.
Has the mass of the copper changed since the start of the experiment?
Results:During the reaction, thegas that is released is hydrogen. The rate at which
the hydrogen is produced increases when the copper pieces (the catalyst) are
added. The mass of thecopper does not changeduring the reaction.
Conclusions:The copper acts as a catalyst during the reaction. Itspeeds up the rate of
the reaction, but is not changed in any way itself.Exercise 3 - 4
- For each of the following, say whether the statement is true or false. If it is false,
re-write the statement correctly.
(a) A catalyst increasesthe energy of reactantmolecules so that a chemical
reaction can take place.
(b) Increasing the temperature of a reaction has the effect of increasing thenum-
ber of reactant particlesthat have more energy that the activation energy.
(c) A catalyst does not become part of the final product in a chemical reaction.- 5 g of zinc granules are added to 400 cm^3 of 0.5 mol.dm−^3 hydrochloric acid. To
investigate the rate of the reaction, the change inthe mass of the flask containing
the zinc and the acid was measured by placingthe flask on a direct reading
balance. The readingon the balance showsthat there is a decreasein mass
during the reaction. The reaction which takesplace is given by the following
equation:
Zn(s) + 2HCl(aq)→ ZnCl 2 (aq) + H 2 (g)(a) Why is there a decrease in mass during the reaction?
(b) The experiment is repeated, this time using 5g of powdered zinc instead of
granulated zinc. How will this influence the rateof the reaction?
(c) The experiment is repeated once more, this time using 5 g of granulated
zinc and 600 cm^3 of 0.5 mol.dm−^3 hydrochloric acid. Howdoes the rate
of this reaction compareto the original reaction rate?
(d) What effect would acatalyst have on the rateof this reaction?(IEB Paper 2 2003)- Enzymes are catalysts. Conduct your own research to find the namesof common
enzymes in the human body and which chemical reactions they play a role in. - 5 g of calcium carbonate powder reacts with20 cm^3 of a 0.1 mol.dm−^3 solution
of hydrochloric acid. The gas that is producedat a temperature of 25circC is
collected in a gas syringe.