CSEC Chemistry:Rates of reaction

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rates of reactions

CSEC Chemistry by naresh birju chapter 12 or Concise Chemistry by Anne tindale chapter 12

START

The correct definition of rate of reaction is the change in concentration of a reactant or product with time at a stated temperature. Click here to see more.

MEASURING RATES OF REACTION

The definition for rate says change in concentration of reactant or product with time but it is very difficult to measure concentration directly. It is easier therefore to measure some other property( like decrease in mass, volume of gas, colour intensity or electrical conductivity) that is PROPORTIONAL TO CONCENTRATION and will change in the same way as the concentration changes

Measuring rates of reaction

APPEARANCE OF A PRECIPITATE

CHANGE IN COLOUR INTENSITY, PRESSURE, TEMPERATURE OR pH can be measured over time if these properties change during the reaction

decrease in mass

Volume of gas

Volume of gas produced over time can be measured USING A GAS SYRINGE if the reaction produces a gas. Click here.

Decrease in mass of the reaction can be measured over time USING A BALANCE if the reaction produces a gas that escapes. Click here

This can be measured once it is formed in the reaction. Click here.

Determining rates of reaction

So what's next? After conducting the experiments as seen on the previous slide, a table of the results obtained is drawn showing the change in property being measured with the time taken for the change. A graph is then plotted with the y axis having the property being measured and the x axis having the change in time

Rate of reaction graph 1

Rate of reaction graph 2

• This graph is obtained if we measure how the concentration of a reactant changes with time

• We will get a downward curve

• The curve gets less steep as the reaction proceeds which means the reaction is slowing down

• This graph is obtained if we measure how the concentration of product changes with time

• We will get an upward curve

• The curve gets less steep as the reaction proceeds which means the reaction is slowing down

VIDEO

Graphical method to determine the rate of the reaction. Refer to page 209 of CSEC Chemistry by Naresh Birju

Collision Theory for reaction rates

For any reaction to occur old bonds must break in reactants and new bonds form in products. Please refer to CSEC Chemistry by Naresh Birju page 204 Concise Chemistry by Anne Tindale page 106

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VIDEO ON COLLISION THEORY OF REACTANTS

FACTORS AFFECTING RATES OF REACTIONS

1..Concentration 2. Temperature 3.Surface area(Particle size) 4. Catalyst

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CHEM-MEME TIME

Effect of factors affecting rate of reaction on the rate of reaction graphs

On page 9, we saw that we can draw graphs to represent data from experiments to show the rate of reaction as seen in the graphs on the top right. We just looked on the last page at different factors affecting rates of reactions. These effects can also be represented on these graphs as shown in the graph on the bottom right of this page.

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SUMMARY VIDEOS (Refer to page 210 of CSEC Chemistry by Naresh Birju)

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CASE CLOSED

THANKS!