Chemistry 2 Lesson 4.1 How fast? AQA Additional Science

Aims Class work 21 September 2007 How fast? LO’s Do all reactions go at the same speed? Write it down!! Page 58 © C Meyer

You have 15 mins to complete Q1-3 What have I learnt?

Chemistry Unit 2 Sections Rates of Energy and Acids, alkalis reaction  reactions  Electrolysis  and salts 4 of 7 © C Meyer

All Know that reactions go at different speeds and they can be measured Most Define rate of reaction List different measurement techniques Some Explain why a certain method is best to use to measure reaction rates Aims

Rate of reaction is just another way of saying how fast is the reaction 1.Give me the fastest and slowest reaction you can think of 2.Give me a biological reaction, is it fast or slow? Do all reactions go at the same speed?

Fast Explosions Fireworks Slow Metal rusting

Do all reactions go at the same speed?

Two common ways: 1) Measure how fast the products are formed 2) Measure how fast the reactants are used up Do all reactions go at the same speed? In a lab chemical reaction, what 2 ways could we measure how fast the reaction is going?

Title – Rate of reaction Can measure how fast reactants used up or products are made Do all reactions go at the same speed? m3 What different ways could we do this with the following reaction? calcium carbonate + hydrochloric acid  calcium chloride + water + carbon dioxide CaCO 3 (s) + 2HCl(aq)  CaCl 2 (aq) + H 2 O(l) + CO 2 (g) What state are chemicals in? (solid, liquid, gas) Use volume of chemical Use mass of chemical

SAFETY Acid - Goggles 20 mins Do all reactions go at the same speed? Need 2 graphs at the end What measurements will you take?

SAFETY Acid - Goggles 20 mins Do all reactions go at the same speed? As the gas given off leaves the flask the total mass of the flask and its contents decreases slightly. Readings of the mass(g) can be taken. Typically at 1 minute intervals. The gas given off can be collected in a syringe and readings taken every 30 seconds or so. TimeReading 0 s0 cm 3 TimeReading 0 s??g Need 2 graphs at the end

Tidy UP!!! Stack items tidily Clean up bench/floor Sit down when finished Draw your graphs Homework Finish off drawing your graphs and label what is going on

Rate of reaction graph Amount of product formed Time Slower reaction Fast rate of reaction here Slower rate of reaction here due to reactants being used up Do all reactions go at the same speed? Dependent v independent??

Rate graphs and reactant concentrations Amount of product Time reactants product Reactant Concentration falls Rate of Reaction falls All product All reactant Mix of reactant And product Gradient of graph decreases

Demo – precipitation If the product is a precipitate there is a third method you can use. Do all reactions go at the same speed? Sodium thiosulphate + hydrochloric acid  sodium chloride + water + sulphur dioxide + sulphur Na 2 S 2 O 3 (aq) + 2HCl(aq)  2NaCl(aq) + H 2 O(l) + SO 2 (g) + S(s) We can how long it takes to produce enough sulphur to make the solution opaque (non see- through). If cross disappears quickly, is the reaction fast or slow?

The End