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Presentation On Factors Affecting The Rate Of Reaction (part 1)

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Published in: Chemistry | Science
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This PPT is suitable for the IGCSE and O Level Chemistry students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Factors Affecting the Rate of Reaction (Part 1) Chemistry (IGCSE / O-Level)
  2. What will you learn in this lesson? • Effect on the rate of reaction of: (a) changing the concentration of solutions (b) changing the pressure of gases (c) changing the surface area of solids (d) changing the temperature • Practical methods for investigating the rate of a reaction including change in mass of a reactant or a product and the formation of a gas • Interpret data, including graphs, from rate of reaction experiments
  3. Reaction Rate A measure of how fast a reaction can take place Following factors influence the rate of reaction: • Concentration effect that brings more reactant molecules together, including: 1. Surface area of any solid reactant 2. Concentration of the reactant solutions 3. Pressure of reacting gas 4. Temperature at which the reaction is carried out • Use of a catalyst
  4. Effect of Reactant Concentration (Surface Area of Reacting Solids) • When one or more of the reactants is solid, the more finely powdered (or finely divided) solid(s) are, the greater the rate of reaction • If a solid is being reacted to liquid (or solution), the greater the surface area, the more solid is exposed to liquid marble surface exposed Increas rea or
  5. Effect of Reactant Concentration (Surface Area of Reacting Solids) • Experimenting the effect of surface area of reacting solid by using marble chips (calcium carbonate) with dilute hydrochloric acid calcium carbonate + hydrochloric acid -9 calcium chloride + water + carbon dioxide cac03(s) + 2HC1(aq) -e caclz(aq) + HzO(1) + C02(g) 20.49 Figure 8.6; Apparatus - rrÆrts A B: the Of The carbon the f' a' k v d a Lite In This detected by the
  6. Effect of Reactant Concentration (Surface Area of Reacting Solids) There are several important points about the graph. 1 2 3 The reaction is fastest at the start. This is shown by the steepness of the curves over the first few minutes. Curve B is steeper than curve A. This means that gas (C02) is being produced faster with sample B. The sample with smaller chips, with a greater surface area, reacts faster. Beyond this part of the graph, both reactions slow down as the reactants are used up (Figure 8.8). The total volume of gas released is the same in both experiments. The mass of CaC03 and the amount of acid are the same in both cases. Both curves flatten out at the same final volume. Sample B reaches the horizontal part of the curve (the plateau) first. A numerical value for the rate of reaction at any given time can be found by drawing a tangent to the curve at that time. The slope of that tangent gives a value for the rate of reaction at that point. A tangent drawn at the start of the curve will give the initial rate of reaction.
  7. Effect of Reactant Concentration (Surface Area of Reacting Solids) reaction has@is-hed formed smill' ch•ngeün «fastest at 'the start iiry amountofpro-duct in larger time large Change tn amumt "small timo Time 8.8: A chemical readon is fastest at the start. It slows down as the readants are used up.
  8. Effect of Reactant Concentration (Concentration of Reacting Solutions) The same reaction between calcium carbonate and hydrochloric acid is taken to measure the effect of concentration of reacting solutions calcium carbonate + hydrochloric acid —9 calcium chloride + water + carbon dioxide cac03(s) + 2HC1(aq) -s cac12(aq) + Hz0(l) + •C02(g) The only difference is the concentration of hydrochloric acid with the same apparatus, volume and amount of reactants gas inge This apparatus could be used to study the rates of other reactions that produce a gas, such as, mg(s) + 2HC1(aq) MOC12(aq) + H2(q)
  9. Effect of Reactant Concentration (Concentration of Reacting Solutions) Time/ s Again. the graph shows some important points. 1 The curve for experiment Cis steeper than for D. This shows clearly that reaction using more concentrated acid, is faster than reaction D. 2 The curve for experiment Cstarts off twice as steeply as for D. This means thatthe reaction in C is twice as fastasin experiment D initially. So, doubling the concentration of the acid doubles the rate of reaction. 3 Thetotal volumeofcarbondioxide produced Is the same in both experiments. Both reactions produce the same volume of gas, although experiment C produces it faster. These results show that the rate of a reaction increases when the concentration of a reactant in solution is increased.
  10. Effect of Reactant Concentration (Pressure of Reacting Gases) • In a reaction involving gases, increasing the pressure has the similar effect as increasing the concentration in a liquid • More pressure, more collision between particles of gas. The gas react more readily, so the rate of reaction is increased • Changing the pressure has no effect on a reaction that involves only solids or liquids 1 kVpp_ Fuel and Gas Compression and Ignition in Car Engine
  11. Effect of Reactant Concentration A reaction can be made go faster or slower by changing the temperature of reactants, such as, the rate of decay and oxidation by the air is slower at lower temperatures sodium thiosulfate + hydrochloric acid sodium chloride + sulfur + sulfur dioxide + water nazS203(aq) + 2HC1(aq) 2NaCl(aq) + SC) + soz(g) + H20(l) ,.cid Same apparatus of previous experiments can be used to measure the effect of temperature on rate of oroduction of gas, but in this exoeriment orecioitation is the indicator
  12. Effect of Reactant Concentration (Effect of Temperature) i rate offeaction I/time The graph shows two important points. 1 The cross disappears more quickly athi#ertemperatures. The shorterthetime neededförthecrossto disappear, the faster the reaction. 2 The curve is not a straight line. These results show that the rate of a reaction increases when the temperature of the reaction mixture is increased.
  13. 1 2 3 Effect of Reactant Concentration (Practice Questions) What will we observe happening to the rate of a Chemical reaction in response to the following? a an increase in temperature b an increasein the surface area of a solid reactant c an increased concentration of a reacting soluüon. Why is perishäble food kept in a refrigerator? When is a chemical reaction at fastest?

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