Rates of Reaction Year 11 Flashcards
what is meant by a rate of reaction
the speed at which a chemical reaction happens
give both formulas for mean rate of reaction with units
amount of reactant used / time taken
amount of product formed/ time taken
rate of reaction is measured in g/s or cm3/s or mol/s
what 5 factors affect the rate of a reaction
- increased concentration (of reactants in a solution)
- increased pressure (of reacting gases)
- increased temperature
- increased surface area (of solid reactants)
- the presence/ use of catalysts
how does surface area affect the rate of a reaction
- the smaller the pieces, the larger the surface area, the faster the rate of reaction
if the solid is split into several pieces, SA increases
any reaction involving a solid can only happen at the surface of the solid
how does concentration affect the rate of a reaction
- the higher the concentration of a dissolved reactant (in liquid), the faster the rate of reaction
how does pressure affect the rate of a reaction
- the higher the pressure, the faster the rate of reaction
how does temperature affect the rate of a reaction
- the higher the temperature, the faster the rate of reaction
what do catalysts do and what happens to them in a reaction?
- speeds up a reaction
- they are not used up in the reaction itself
- they decrease the activation energy needed for the reaction to occur
draw diagrams to represent the effect of a low and high concentration on a reaction
LOW………………………………………….HIGH
. O I O O
. O I O O
. O I O O O
. O I O O
. O I O O O O
. O I O O
. O I O O O
more particles = more collisions
what type of collision between particles can allow for a chemical reaction to occur?
-reactant particles must collide
in terms of particles, how does increasing the temperature affect the rate of reaction?
- at a higher temperature, particles have more energy so move faster and are more likely to collide
- the particles collide with more energy so the number of successful collisions increases
how do catalysts affect the rate of reaction?
- they provide alternative reaction pathway creating more collisions, meaning a higher rate of reaction
in terms of particles, how does increasing the concentration affect the rate of reaction?
- at a higher concentration, there are more particles in the same amount of space
- this means the particles are more likely to collide therefore more likely to react
in terms of particles, how does increasing the surface area affect the rate of reaction?
- if the solid is split into several pieces, the SA increases meaning there is an increased area for the reactant particles to collide with
- the smaller the pieces the larger the surface area meaning more collisions so a greater chance of reaction
in terms of particles, how does increasing the pressure affect the rate of reaction?
- as the pressure increases, the space which the gas particles are moving becomes smaller
- the gas particles become closer together, increasing the frequency of collisions meaning particles are more likely to react
what is meant by the term activation energy? why do particles need this energy
- the minimum amount of energy that particles must have if they are to react when they collide.
- particles need this much energy to break the bonds in the reactants & start the reaction
which reaction would have the fastest rate, A or B and why?
A) 2g solid strip of Mg with water
B) 2g powdered Mg with water
- B
- powder has a higher surface area to volume ratio than the solid strip
which reaction would have the fastest rate, A or B and why?
A) 2mol/dm3 HCL with excess ethanoic acid
B) 4mol/dm3 HCL with excess ethanoic acid
- B
- 4mol/dm3 HCL solution is more concentrated than the 2mol/dm3 HCL solution
what is collision theory
the idea that the rate of a reaction depends on:
- the frequency of collisions btwn particles. more collisions = faster reaction
- the energy with which particles collide
The collision between the molecules in a chemical reaction provides the kinetic energy needed to break the necessary bonds so that new bonds can be formed.
how could you calculate the rate of reaction at a specific time?
- draw a tangent to the curve at the specific time
- construct a right angled triangle using the the tangent as the longest side
- change in y (product)/change in x (time)
calculate the rate of reaction btwn CaCO3 and HCL in which 0.6g of CaCO3 was used up after 2.5 mins
0.6/2.5 = 0.24g/min
calculate the rate of reaction btwn Li and H2O in which 2.5 x 10^-3 moles of H2 was produced in 10 seconds
(2.5 x 10^-3)/10 = 0.00025 mol/sec
calculate the rate of the decomposition of hydrogen peroxide (H2O2) in which 15cm of O2 was produced after 6 mins
15/6 = 2.5cm3/min
name the salt produced in the reaction between zinc granules and sulfuric acid
zinc sulfate
what are the main methods for meausring the rate of reaction
- measuring the increasing volume of a gas given off
- measuring the decreasing mass of a reaction mixture
- measuring the decreasing light passing through a solution
what would the gradient look like on a graph showing the decreasing mass of a reaction mixture
- steep gradient to start showing a fast reaction
- shallow gradient at the end showing a slow reaction
what would the gradient look like on a graph showing the increasing mass of a reaction mixture
- shallow gradient to start showing a slow reaction
- steep gradient at the end showing a fast reaction
what happens if particles collide with less energy than the activation energy?
they will not react and will just bounce off each other
what would the gradient show on a graph showing the rate of a reaction
steep slope = fast reaction
shallow slope = slow reaction
no slope = no reaction
what happens in terms of particles and reactants as a reaction progresses
- the concentration of reactants decreases
- this reduces the frequency of collisions btwn particles so the reaction slows down & stops
how do catalysts decrease the activation energy needed for a reation to occur?
by providing an alternative reaction pathway meaning a lower activation energy is required for the reaction to occur
state two properties of the collisions between particles that affect the rate of a reaction
- the frequency of collisions
- the energy with which particles collide
use collision theory to explain why increasing the concentration of a reactant increases the rate of reaciton
- there are more particles in a given volume so the collisions btwn particles are more frequent
explian why cutting the reactant (magnesium) into smaller pieces increases the rate of reaction
- smaller pieces have a higher surface area to volume ratio
- for the same volume of solid the particles around it have more area to work on so collisions will be more frequent
how would you expect a reaction to change if the reactant (magnesium) was cut into smaller pieces
it would increase
other than changing the concentration and size of reactant, what other change could be made to change the rate of reaction?
changing the temperature
adding a catalyst
explain using collision theory if increasing the volume of a reaction vessel would increase the rate of reaction
- increasing the volume decreases the pressure of the reacting gases
- the particles would be more sprea out so would collide less frequently
- therefore the reaction rate decreases not increases
explain using collision theory if increasing the temperature at which a reaction is carried out would increase the rate of reaction
- increasing the temperature causes the particles the move faster so the frequency of collisions increases
- therefore the rate of reaction increases
when cerium oxide is mixed with hydrogen and iodine gases the rate of reaction increases. what does this suggest about cerium oxide?
it is a catalyst
will the reaction equation change if a catalyst is present in the reaction vessel. why?
- it wont change.
- the catalyst inst used up in the reaction so wont appear in the reaction equation
how is the rate of reaction measured?
dividing the amount of reactants used up or products formed by the time taken for the reaction complete
which do you take measurements of to work out the rate of reaction:
- mass
- volume of solution
- volume of gas
- frequency?
mass
volume of gas
a student times how long it takes for a solution to go cloudy at certain temperatures to investigate how the rate of reaction is affected by temperature
identify the dependent, independent and one controlled variable in this experiment
dependent - time taken for solution to go cloudy independent - temperature controlled - volume of the reactants
define a dependent variable
- the variable being tested and measured in an experiment.
- As the independent variable is changed the change in the dependent variable is observed and recorded.
define a independent variable
- the variable that is changed or controlled in an experiment.
- variables that the experimenter changes to test their dependent variable
define a controlled variable
- the variable which is constant and unchanged throughout the course of the experiment
in an experiment, a gas is produced.
- would it be more accurate to measure the rate of reaction by timing how long it take for the solution to go cloudy or how long it takes a volume of gas to be produced? why?
- volume of gas to be produced bc this method is less subjective ie a gas syringe
