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chemistry > Rates of Reaction Year 11 > Flashcards

Rates of Reaction Year 11 Flashcards

1
Q

what is meant by a rate of reaction

A

the speed at which a chemical reaction happens

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2
Q

give both formulas for mean rate of reaction with units

A

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

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3
Q

what 5 factors affect the rate of a reaction

A
  • 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
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4
Q

how does surface area affect the rate of a reaction

A
  • 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

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5
Q

how does concentration affect the rate of a reaction

A
  • the higher the concentration of a dissolved reactant (in liquid), the faster the rate of reaction
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6
Q

how does pressure affect the rate of a reaction

A
  • the higher the pressure, the faster the rate of reaction
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7
Q

how does temperature affect the rate of a reaction

A
  • the higher the temperature, the faster the rate of reaction
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8
Q

what do catalysts do and what happens to them in a reaction?

A
  • speeds up a reaction
  • they are not used up in the reaction itself
  • they decrease the activation energy needed for the reaction to occur
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9
Q

draw diagrams to represent the effect of a low and high concentration on a reaction

A

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

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10
Q

what type of collision between particles can allow for a chemical reaction to occur?

A

-reactant particles must collide

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11
Q

in terms of particles, how does increasing the temperature affect the rate of reaction?

A
  • 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
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12
Q

how do catalysts affect the rate of reaction?

A
  • they provide alternative reaction pathway creating more collisions, meaning a higher rate of reaction
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13
Q

in terms of particles, how does increasing the concentration affect the rate of reaction?

A
  • 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
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14
Q

in terms of particles, how does increasing the surface area affect the rate of reaction?

A
  • 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
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15
Q

in terms of particles, how does increasing the pressure affect the rate of reaction?

A
  • 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
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16
Q

what is meant by the term activation energy? why do particles need this energy

A
  • 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
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17
Q

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

A
  • B

- powder has a higher surface area to volume ratio than the solid strip

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18
Q

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

A
  • B

- 4mol/dm3 HCL solution is more concentrated than the 2mol/dm3 HCL solution

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19
Q

what is collision theory

A

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.

20
Q

how could you calculate the rate of reaction at a specific time?

A
  • 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)
21
Q

calculate the rate of reaction btwn CaCO3 and HCL in which 0.6g of CaCO3 was used up after 2.5 mins

A

0.6/2.5 = 0.24g/min

22
Q

calculate the rate of reaction btwn Li and H2O in which 2.5 x 10^-3 moles of H2 was produced in 10 seconds

A

(2.5 x 10^-3)/10 = 0.00025 mol/sec

23
Q

calculate the rate of the decomposition of hydrogen peroxide (H2O2) in which 15cm of O2 was produced after 6 mins

A

15/6 = 2.5cm3/min

24
Q

name the salt produced in the reaction between zinc granules and sulfuric acid

A

zinc sulfate

25
Q

what are the main methods for meausring the rate of reaction

A
  • 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
26
Q

what would the gradient look like on a graph showing the decreasing mass of a reaction mixture

A
  • steep gradient to start showing a fast reaction

- shallow gradient at the end showing a slow reaction

27
Q

what would the gradient look like on a graph showing the increasing mass of a reaction mixture

A
  • shallow gradient to start showing a slow reaction

- steep gradient at the end showing a fast reaction

28
Q

what happens if particles collide with less energy than the activation energy?

A

they will not react and will just bounce off each other

29
Q

what would the gradient show on a graph showing the rate of a reaction

A

steep slope = fast reaction
shallow slope = slow reaction
no slope = no reaction

30
Q

what happens in terms of particles and reactants as a reaction progresses

A
  • the concentration of reactants decreases

- this reduces the frequency of collisions btwn particles so the reaction slows down & stops

31
Q

how do catalysts decrease the activation energy needed for a reation to occur?

A

by providing an alternative reaction pathway meaning a lower activation energy is required for the reaction to occur

32
Q

state two properties of the collisions between particles that affect the rate of a reaction

A
  • the frequency of collisions

- the energy with which particles collide

33
Q

use collision theory to explain why increasing the concentration of a reactant increases the rate of reaciton

A
  • there are more particles in a given volume so the collisions btwn particles are more frequent
34
Q

explian why cutting the reactant (magnesium) into smaller pieces increases the rate of reaction

A
  • 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

35
Q

how would you expect a reaction to change if the reactant (magnesium) was cut into smaller pieces

A

it would increase

36
Q

other than changing the concentration and size of reactant, what other change could be made to change the rate of reaction?

A

changing the temperature

adding a catalyst

37
Q

explain using collision theory if increasing the volume of a reaction vessel would increase the rate of reaction

A
  • 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
38
Q

explain using collision theory if increasing the temperature at which a reaction is carried out would increase the rate of reaction

A
  • increasing the temperature causes the particles the move faster so the frequency of collisions increases
  • therefore the rate of reaction increases
39
Q

when cerium oxide is mixed with hydrogen and iodine gases the rate of reaction increases. what does this suggest about cerium oxide?

A

it is a catalyst

40
Q

will the reaction equation change if a catalyst is present in the reaction vessel. why?

A
  • it wont change.

- the catalyst inst used up in the reaction so wont appear in the reaction equation

41
Q

how is the rate of reaction measured?

A

dividing the amount of reactants used up or products formed by the time taken for the reaction complete

42
Q

which do you take measurements of to work out the rate of reaction:

  • mass
  • volume of solution
  • volume of gas
  • frequency?
A

mass

volume of gas

43
Q

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

A 
dependent
- time taken for solution to go cloudy
independent
- temperature
controlled
- volume of the reactants
44
Q

define a dependent variable

A
  • 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.

45
Q

define a independent variable

A
  • the variable that is changed or controlled in an experiment.
  • variables that the experimenter changes to test their dependent variable
46
Q

define a controlled variable

A
  • the variable which is constant and unchanged throughout the course of the experiment
47
Q

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?

A
  • volume of gas to be produced bc this method is less subjective ie a gas syringe

chemistry (9 decks)

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