chemistry - rates of reaction & energy changes: rates of reaction (7.1 - 7.8)

7.1 core practical: effects of changing conditions of reaction on rates of chemical reactions - measure production of gas (reaction between hydrochloric acid & marble chips)

1. set up apparatus shown in diagram

2. measure 40cm³ dilute hydrochloric acid into conical flask

3. add 5g small marble chips to flask

4. immediately stopper flask & start stop clock

5. record total volume of gas produced every 30 secs until reaction finished

6. repeat experiment using 5g larger marble chips

smaller chips = larger surface area = faster rate of reaction

7.1 core practical: effects of changing conditions of reaction on rates of chemical reactions - observe colour change (reaction between sodium thiosulfate & hydrochloric acid)

1. place 50cm³ sodium thiosulfate into 300cm³ conical flask

2. measure 5cm³ dilute hydrochloric acid in test tube

3. clamp conical flask in water bath at certain temp. & record temp.

4. place test tube in rack in same water bath

5. after 5 mins remove flask & place on white piece of paper marked with cross

6. add acid to thiosulfate & start stop clock

7. look down from above, stop clock when cross disappears

8. record this time & record final temp. of mixture

9. repeat at 3 or 4 other temps. between 20°C & 50°C

higher temp. = more frequent successful collisions = faster rate of reaction

7.2 practical methods for determining rate of given reaction

measure changes in:

• concentration

• mass/volume of reactants/products

e.g. measure mass of reactant used if product is gas: do experiment on weighing scales, measure how much mass lost

e.g. measure volume of product formed if product is gas: collect gas produced in gas syringe, shows volume gas produced

rate of reaction formulas

amount of reactant used/time

amount of product formed/time

units: g/s; cm³/s

7.3 what do particles have to do for reaction to occur & why?

collide with enough energy

successful collision - energy helps break bonds, atoms rearranged to make products

activation energy

minimum amount of energy needed by colliding particles for reaction to occur

7.3 frequency &/or energy of collisions effect on rate of reaction & why

frequency &/or energy of collisions increased = rate of reaction increased

more collisions/more particles with activation energy required = more reactions

7.4 change in temperature effect on rate of reaction

temperature increased = rate of reaction increased

reactant particles speed up & have more energy = more frequent collisions, more particles have enough energy to react when collide

7.4 change in concentration effect on rate of reaction

concentration of solution increased = rate of reaction increased

more reacting particles in same volume = more frequent collisions

7.4 change in surface area:volume of solid effect on rate of reaction

surface area:volume ratio of solid increased = rate of reaction increased

• decrease size of solid pieces, keep total volume of solid same

more surface area for collisions to occur = more frequent collisions

7.4 change in pressure (reactions involving gases) effect on rate of reaction

pressure of gases increased = rate of reaction increased

reactant particles closer together = more frequent collisions

7.5 graphs of mass/volume/concentration of reactant/product against time

gradient indicates rate of reaction: steeper gradient = faster rate of reaction

7.6 catalysts

substances that speed up rate of reaction

don’t alter products of reaction

not chemically changed themselves

in mass at end of reaction

7.7 adding catalyst effect on rate of reaction & why (activation energy)

increases rate of reaction

provides alternative reaction route - requires less activation energy

7.8 what are enzymes? (b... c...)

biological catalysts

7.8 what are enzymes used in production of?

alcoholic drinks