How can I slow the rate of this reaction down? Starter: What does rate mean?

Learning objectives: To know what is meant by rate of reaction. To know how particle size affects the rate of a reaction. Key words: rate of reaction, particle size Rates of reaction

We are going to investigate how particle size affects rate – Ac6.5 PARTICLE SIZE can also be thought of as SURFACE AREA: The smaller the particle size, the greater the surface area available for a reaction. Just think, if you cut a strawberry or apple up into small pieces, does it go mouldy faster or slower than when left whole? What happens to the rate of the reaction? vs

Very fast Slow Surface area Small surface area for a reaction BUT large particle size Large surface area for a reaction BUT small particle size

Learning objectives: To be able to describe how concentration affects the rate of a reaction. Key words: rate of reaction, concentration Rates of reaction

Concentration The more crowded (concentrated) the solution, the faster the reaction. Collisions infrequentCollisions frequent

Learning objectives: To be able to explain how temperature affects rate of reaction. Key words: rate, temperature Rates of reaction

1.Place 20cm 3 of sodium thiosulphate (Na 2 S 2 O 3 ) and 20cm 3 water in a boiling tube. 2.Place 10cm 3 HCl in a conical flask. 3.Place the conical flask on the black cross. 4.Add the contents of the boiling tube to the flask and start the timer. 5.Watch from the top of the flask until the solution has gone cloudy (this is the end of the reaction). 6.Stop the timer and record the time. Na 2 S 2 O 3 (aq) + 2HCl (aq) 2NaCl (aq) + SO 2 (aq) + S (s) +H 2 O (l) Investigating temperature

Temperature More collisions per second Fewer collisions per second

Learning objectives: To know how catalysts increase the rate of a reaction. Key words: rate, catalyst Rates of reaction

Catalysts For chemical reactions to occur: Bonds in the reactants have to begin to break so that new bonds (in the products) can form. Molecules must collide in a way that lets the reacting parts of the molecules come together. Catalysts can help with either or both of these processes. A catalyst is a substance that speeds up a reaction without getting used up in the process.

Learning objectives: To be able to draw a graph of a rate experiment. To be able to explain why rate changes. Key words: rate of reaction, collision theory Rates of reaction Starter: Name 3 ways rate can be increased.

Time / seconds Volume / cm3 Which plot shows a reaction carried out at a higher temperature?

Learning objectives: To be able to draw a graph of a rate experiment. To be able to explain why rate changes with changes in reaction conditions. Key words: rate of reaction, collision theory W:\Chemistry\year 10\Rates of Reaction notes Rates of reaction

Most reactions are exothermic (give out heat) overall but there is still a need for energy to get the reaction started. Energy in chemicals Reaction Activation energy Break old bonds Energy taken in Form new bonds Energy given out Activation energy

How do reactions happen? Particles must collide AND with a certain amount of energy. This is COLLISION THEORY. The smallest amount of energy needed for any one reaction is called the ACTIVATION ENERGY (Ea). The rate of a reaction depends on 2 things: 1. The frequency of particle collisions 2. The energy of the collisions

A pupil performed an investigation into the rate of reaction between a metal and an acid. The results below where obtained. i) Plot a graph of gas volume (y-axis) against time (x-axis) ii) When was the rate of reaction fastest? iii) Use the graph to find the volume of gas produced after 35 seconds. iv) Use the graph to tell after how long the reaction stopped. v) On the same graph, now plot the data collected when the acid was 2M concentration. What has happened to the gradient and so the rate? Activity Concentration of acid = 1M

Do reactions just keep going at the same speed? 100%25%50%75% percentage completion of reaction 0% reactants product

Graphing rates of reaction

Factors that affect the rate of a reaction Temperature Concentration Particle size Pressure - Gases Adding a catalyst

Reaction rate is increased by…. Increasing temperature Increase concentration of reactants Decreasing particle size – increase surface area Increase pressure - Gases Adding a catalyst

Experimental Results Time / seconds Volume / cm3 ii) The reaction was fastest at about 25 seconds as the gradient of the line is highest at this point. iii) About 175 cm 3 iv) About 55 seconds. v) Higher concentration reaction is sketched in red. Answer

A pupil performed an investigation into the rate of reaction between a metal and an acid. The results below where obtained. Activity Concentration of acid = 1M Concentration of acid = 2M

Results and analysis Where do I plot error bars? Plot a scatter graph of your raw data showing the spread/range of each time result for each concentration and the average value (plotted here)

Results and analysis Time (s) Volume CO 2 (cm 3 ) 1M HCl 2M HCl Gradient of tangent at (time = 0) = rate …or average rate = 1/time for particular volume of gas t 1 Rate = 1/t 1 t 2 Rate = 1/t 2 Where do a plot error bars? Plot a scatter

Activity: Plotting experimental data and explaining quantitative relationships. Concentration (% HCl) Rate (1/t) Plot the data in the table above. 2.Fully label your graph using the investigation criteria. 3.Describe any trend seen in your data. 4.Find the equation of the line. 5.Describe AND explain the quantitative relationship between concentration and rate of reaction. 6.Swap your graph with a neighbour and mark their graph using the investigation criteria for the I strand.

Activity: Plotting experimental data and explaining quantitative relationships.

Powdered calcium carbonate has a greater SA  more collisions per second with HCl  more collisions per second having E ≥ Ea Use collision theory to answer the following… 1(b) Explain why hydrochloric acid reacts faster with powdered calcium carbonate than it does with lumps of calcium carbonate. 1(a) The collision theory states that reactions can only occur when particles collide. Give a reason why collisions between particles do not always lead to a reaction. Energy of collision may be LESS than activation energy of the reaction

Rate increases because the TOTAL number of collisions per second increases. So, greater number of collisions have energy ≥ Ea Rate increases because the % of molecules with energy greater than activation energy increases. So, greater number of collisions per second with energy ≥ Ea 1(d)State and explain the effect on rate of increasing the temperature. 1(c)State and explain the effect on rate of increasing the concentration of a reactant.