Topic 6 - Rates of Reaction Flashcards
what is the mean rate of reaction?
reactant used OR product formed / time
what are the 3 ways of measuring rate of reaction?
- precipitation
- change in mass
- volume of gas given off
advantages of precipitation
- simple
- easy to carry out
disadvantages of precipitation
- only works for reactions where there’s a visual change
- results are subjective as people may disagree when the mark ‘disappears’
- can’t plot rate of reaction graph
advantages of change in mass
- most accurate as the mass balance very accurate
- easy to carry out
- can plot a rate of reaction graph
disadvantages of change in mass
- releases the gas straight into the room
- if gas is harmful, carry out the reaction in a fume cupboard
advantages of volume of gas
- can plot a rate of reaction graph
- gas syringes give volumes to nearest cm3 : very sensitive
- gas isn’t released into the room
disadvantages of volume of gas
- if the reaction is too vigorous you can blow the plunger out the end of syringe
- quite hard to set up: lot of equipment
what do reaction graphs with a fast rate of reaction look like
- it has the steepest curve at the beginning
- shows products are being formed more quickly
- takes a shorter time to level off
( plateau )
what do reactions with more reactants look like
- they plateau off at a higher level as a higher amount of products are being formed
why does the rate of reaction decrease over time?
- the rate of a reaction is directly proportional to the concentration of reactants.
- As the reaction proceeds, the reactants are converted into products,
- which causes the concentration of reactants to decrease
- and the rate of the reaction to slow down
factors that affect the rate of reaction:
- temperature
- concentration
- surface area
collision theory
( 2 things )
- for particles to react they have to collide with each other with sufficient energy
- this is called the activation energy
- the more frequent the collisions are, the faster the rate of reaction
temperature ( frequency of reactions )
- when temp increased, particles move quicker
- this means they will collide more frequently which means faster rate of reaction
temperature ( activation energy )
- increasing temp also increases amount of energy particles have
- more particles will have activation energy required
- more successful reactions
concentration
- more concentrated means the particles of the reactant are more densely packed together
- leads to more frequent collisions between the relevant particles
- rate of reaction will increase
surface area
- a greater surface area means the particles around it in solution will have more area to work on
- this leads to more frequent collisions
- rate of reaction will increase
how to increase SA : V ratio of substances
- if it is a solid, crushing it into a powder increases SA : V ratio
rate and proportionality
the rate of the reaction is directly proportional to the frequency of successful collisions
what are catalysts?
a substance which can speed up the rate of reaction without being used up or changing the reaction products
how do catalysts speed up the rate of reaction?
- it provides an alternative reaction pathway with a lower activation energy
- more particles have the required activation energy leading to more successful collisions
what are enzymes?
- BIOLOGICAL catalysts that speed up rate of reactions in living organisms
what are yeast cells used for?
- zymases are enzymes from yeast cells
- catalyse the reaction that converts sugars into ethanol and carbon dioxide
- fermentation
