 Rate Of Reaction & Temperature Noadswood Science, 2012

Monday, September 14, 2015  To understand how temperature affects the rate of reaction

Reaction  How do we know if a reaction has taken place?  Color change  Gas given off  Precipitate forms  Temperature change  pH change

Rate Of Reaction  A variety of factors affect the rate of reaction, including: -  Temperature  Concentration of a dissolved reactant  Pressure of a reacting gas  Surface area of reactants  Catalysts

Particles  How do the particles differ in cold water and boiling water?  In boiling water the particles collide more often and with more force – they are moving quicker and with more energy…

Collision Theory  Particles need to collide with enough energy (activation energy) to react  This activation energy is needed to break the bonds in the reactants – reactions only occur it the particles have enough initial ‘activation energy’

Collisions  Chemical reactions occur when particles of reactant collide with enough energy to react  Anything that increases the chance of effective collision increases the rate of reaction (e.g. surface area, temperature, pressure, using a catalyst etc…)

Collisions  If the temperature is increased:  The reactant particles move more quickly  More particles have the activation energy or greater  The particles collide more often, and more of the collisions result in a reaction  The rate of reaction increases

Equation  The rate of reaction can be worked out simply, recording either the amount of reactant used / product formed and the time taken… Rate of reaction = amount of reactant used or amount of product formed time taken

Experiment  Plan and carry out an experiment investigating how temperature affects the rate of reaction (record your results)…  Measure 50cm 3 sodium thiosulfate into a conical flask  Heat the sodium thiosulfate to the required temperature  Add 5cm 3 hydrochloric acid and begin timing whilst swirling the flask (stop the clock when the cross disappears)  Repeat using different temperatures  Graph your results and write a conclusion

Experiment Temperature ( o C) Time for cross to disappear (sec) Test 1Test 2Test 3Average 30 o C 40 o C 50 o C

Experiment  Why did the cross fade quickest with the highest temperature?  Why did the cross fade?  Was this a fair experiment?

Experiment sodium thiosulphate + hydrochloric acid → sodium chloride + sulphur dioxide + sulphur + water 2HCl + Na 2 S 2 O 3 → 2NaCl + SO 2 + S + H 2 O  The cross faded quickest when the temperature was greatest as a temperature increases will increase the rate of reaction – this is because the particles are moving quicker and with more energy, increasing both the chance the particles collide and the force at which they do  The cross fades as a sulfur forms (this is solid and causes the solution to go cloudy), although it is difficult to swirl with the same amount of force, so this would make our experiment unreliable!

Collisions  At higher temperatures molecules move faster – as a result there are more collisions per second and so a faster reaction occurs

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