1.Chemistry > 3.1.9 Rate Equations > Flashcards

3.1.9 Rate Equations Flashcards

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1
Q

define the rate of reaction

A

the change in concentration of a reactant or product per unit of time - change in conc. / time

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2
Q

what are the units for the rate of reaction

A

mol dm^-3 s^-1

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3
Q

define activation energy

A

the minimum energy required for a reaction to occur

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4
Q

what is the rate determining step

A

the slowest step of a reaction

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5
Q

what is collision theory

A

For a reaction to occur: reactants must collide in the correct orientation and with enough energy to react (to break the bonds in the reactants)

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6
Q

what does the total area under the graph of a maxwell boltzmann curve represent

A

represents the total number of particles in the distribution

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7
Q

draw and label a maxwell boltzmann curve

A
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8
Q

draw a maxwell boltzmann curve showing the effect of change in temperature

A
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9
Q

draw a maxwell boltzmann curve showing the effect of change in total number of particles

A
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10
Q

draw a maxwell boltzmann curve showing the effect of using a catalyst

A
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11
Q

how does temperature affect the rate of reactions

A
  • increasing the temperature increase the rate of reaction
  • at higher temperature, more particles have E≥Ea
  • there are more frequent successful collisions
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12
Q

how does concentration of reactants affect rate of reaction

A
  • increasing the concentration of reactants increases the rate of reaction
  • there are more reactant particles within the same volume
  • there are more collisions between reactant particles
  • there are more frequent successful collisions
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13
Q

how does size of reactant particles affect rate of reaction

A
  • breaking a solid reactant into smaller particles increases the rate of reaction
  • there is an increased surface area
  • there are more collisions between reactant particles
  • there are more frequent successful collisions
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14
Q

how do catalysts affect rate of reaction

A
  • using a catalyst increases the rate of reaction
  • catalysts provide an alternative reaction pathway (mechanism) with a lower activation energy
  • catalysts are not used up during a reaction
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15
Q

what is the rate of reaction determined by

A

the rate of the slowest step; only changes which affect the slowest step will have any significant impact on the rate of the reaction

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16
Q
A
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17
Q

what do rate equations show

A

how the rate of a reaction is affected by the concentration of the different chemicals involved in the reaction

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18
Q

what does k stand for in rate equations

A

rate constant - has constant value as long as the temperature and activation energy for the reaction don’t change

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19
Q

what do the orders of a reaction show

A

The relationship between changes in concentration of a reactant and changes in the rate of reaction is known as the order of reaction.

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20
Q

what does zero order mean

A

The relationship between changes in concentration of a reactant and changes in the rate of reaction is known as the order of reaction.

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21
Q

how do you write zero order in a rate equation

A
  • The reactant would not appear in the rate equation.
  • Rate = k[A]⁰
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22
Q

what does first order mean

A
  • Changes in concentration of reactant also happen to the rate of reaction e.g. if the reactant conc. doubles, the rate also doubles
  • Change in concentration is directly proportional to the change in the rate
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23
Q

how do you write first order in a rate equation

A

Rate = k[A]

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24
Q

what does second order mean

A
  • Rate of reaction changes by concentration squared
  • Change in concentration results in rate being multiplied by (change in conc.)²
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25
how do you write second order in a rate equation
Rate = k[A]²
26
if rate = k[B]²[H+] calculate overall order
2 + 1 = 3
27
how do you determine orders of reaction
- To investigate the order of reaction experimentally you need to determine how the rate of a reaction varies as the reactant concentration changes. - Given that rates of reaction are the change in concentration per unit time, you need some way of measuring the concentration of one of hte reactants or products. - Often you can't measure concentration directly and have to measure a physical property that is related to the concentration of one of the reactants or products
28
how would you measure rate of this reaction 2Na(s) + 2HCl(aq) ⇒ 2NaCl(aq) + H2(g)
- Collect hydrogen gas in a gas syringe - Measure volume of gas produced over time - HCl is acid - monitor pH
29
how would you measure rate of this reaction CH3CH2Br + NaOH ⇒ CH3CH2OH + NaBr
Can measure [NaOH] as it is an alkali - Titrate with HCl (or use pH meter??)
30
how would you write this rate equation H2SO4(aq) + BaCl2(aq) ⇒ BaSO4(s) + HCl(aq)
Precipitate will start to make solution opaque as it is produced - Could measure opacity of solution
31
what is the initial rates method
- Repeat a chemical reaction multiple times with different reactant concentrations and measure the rate of reaction each time to find out how changes in the reactant concentration affect the rate of reaction. - multiple experiments; 1 reading
32
what is the problem with the initial rates method and how do you deal with this
the rate will decrease over time as the reactants are used up; to ensure consistency between each repeat experiment, it is common practice to measure the rate of a reaction at the very start (time = 0). This will be the fastest rate, so biggest number, so easier to measure. The concentration of each reactant is known at the start of the reaction, which is essential to analyse how altering the reactant concentrations affects the rate of reaction.
33
draw a graph for an initial rates experiement
34
what do you measure in an intial rates method
It is standard practice to measure the time taken to produce a certain amount of product, which is indicated by a physical property of that product. How much product is actually produced doesn't need to be calculated, so long as the same amount is produced every time the experiment it repeated
35
what is the equation for the Thiosulphate and acid reaction
Na2S2O3(aq) + 2 HCl(aq)⇒ 2 NaCl(aq) + SO2(g) + S(s) + H2O(l)
36
draw a diagram showing the Thiosulphate and acid reaction practical
37
what are the control variables for the Thiosulphate and acid reaction practical
- Mass of sulphur required to obscure cross - Total solution volume and container used for reaction (different containers will have different path lengths) - Concentration of other reactants
38
How would you investigate the order of this reaction (Na2S2O3(aq) + 2 HCl(aq)⇒ 2 NaCl(aq) + SO2(g) + S(s) + H2O(l)) with respect to the different reactants?
- Repeat the experiment using different concentrations of Na2S2O3 or HCl - See if time taken to produce enough S ppt to obscure cross changes
39
draw an example results table for the Thiosulphate and acid reaction practical
40
Why is water added to the reaction mixture in the Thiosulphate and acid reaction practical?
- So the total volume of the reaction mixture is constant - Therefore, any change in reactant volume is proportional to change in reactant conc
41
Why can you analyse the effect of changing the volume of S2O3^2− on rate of reaction instead of calculating the [S2O3^2−]?
Total volume is constant, so change in volume of S2O3^2− is proportional to change in [S2O3^2−]
42
what are the two equations for the iodine-clock experiemnt
- H2O2(aq) + 2I−(aq) + 2H+(aq) ⇒ I2(aq) + 2H2O(l) - 2S2O3^2−(aq) + I2(aq) ⇒ 2I−(aq) + S4O6^2−(aq)
43
draw a diagram for the iodine clock experiemnt
44
At what point in the reaction does the solution turn blue-black in the iodine clock experiment?
- When enough I2 has been produced to react with all the thiosulphate ions - Blue-black colour produced as I2 now reacts with starch
45
Why are most of the reactants combined into one container before starting the reaction in the iodine clock experiment?
So that you don’t have to add five reactants to one container simultaneously to start the reaction
46
Why is hydrogen peroxide added last to the reaction solution in the iodine clock experiemtn?
To prevent the reaction from starting until you are ready to time it
47
Which other reactants could be added last instead of hydrogen peroxide in the iodine clock experiemnt?
Sodium/potassium iodide or sulphuric acid
48
Why is water added to the reaction mixture in the iodine clock experiemnt?
- So the total volume of the reaction mixture is constant - Therefore, any change in reactant volume is proportional to change in reactant conc.
49
Why is a constant volume of Na2S2O8 used in the iodine clock experiment?
So the amount of I2 that must be produced to give the blue-black colour is always the same
50
If you wanted to investigate the order of reaction with respect to H2O2, how would the results table look different in the iodine clock experiment?
- The volume of H2O2 would vary for each run - The volume of Na2S2O8 would be constant for each run
51
draw an example results table for the iodine clock experiment
52
Explain, giving brief experimental details, how you could use a series of experiments to determine the order of this reaction (H2O2(aq) + 2I−(aq) + 2H+(aq) ⇒ I2(aq) + 2H2O(l)) with respect to H2O2 [6 marks]
- Measure 5cm3 of H2O2, 25cm3 of H2SO4, 1cm3 of starch, 20cm3 of water, and 5cm3 of Na2S2O3 - Measure 10cm3 of KI into a different beaker - Add Beaker A to Beaker B and start time immediately - Stir the solution continuously until blue-black colour is produced. Once produced, stop timer. - Record time taken. - Increase volume of H2O2 by 5cm3 and decrease volume of water by 5cm3 to ensure the total volume is constant. Repeat experiment until 0cm3 of water and 25cm3 of H2O2 are added. - Use a water bath to keep temperature consistent - 1/ time taken is a measure of the rate - Plot a graph of 1/time against volume of H2O2 - If graph gives horizontal line, H2O2 is 0 order. If graph gives diagonal line, H2O2 is 1st order. If grave gives upward curving line, H2O2 is 2nd order.
53
what 3 types of graph may be produced from an initial rates experiemnt
54
what is a continuous monitoring method
- 1 experiment; multiple reasings - Measure the concentration of one of the reactants throughout the course of the reaction (i.e. you continuously monitor the reactant concentration). - There is no need to repeat the experiment - The method you use to monitor the reactant concentration depends on the properties of that reactant.
55
how would you complete continuous monitoring with this recation H2O2(aq) + 2H+(aq) + 2I–(aq) ⇒ I2(aq) + 2H2O(l)
Acid concentration can be determined directly by titration with a base
56
why is Monitoring the Concentration of an Acid in continuous monitoring method difficult
titrations are not quick and the acid concentration needs to be monitored regularly.
57
how would you take titrations of a reaction?
58
What is quenching a reaction?
Slowing the rate of reaction down so much that the reaction effectively stops
59
Why would you quench a reaction?
So that you can stop a reaction at a specific time and then analyse it later; to determine a specific concentration at a given time
60
How can you quench a reaction?
- Add reaction to a large volume of water - decreases reactant concentrations - Cool reaction down (decrease temperature) - decreases the number of reactant particles with E greater than or equal to Ea - Remove catalyst by reacting it with another chemical - increases activation energy for the reaction
61
how would you perform continuous monitoring on this reaction CH3COCH3(aq) + I2(aq) ⇒ CH3COCH2I(aq) + HI(aq)
62
How could you quench the acid-catalysed reaction between propanone and iodine?
- Add reaction mixture to an excess of NaHCO3 solution - Neutralises the acid catalyst
63
how do you find the order of a reaction from the results of continuous monitoring
To determine the order of reaction, you plot the change in concentration of the reactant you measured against time.
64
how do you distinguish between first and second order on a graph
65
Consider the reaction below. How could you ensure that the rate of reaction depends only upon the concentration of H+ in the reaction: H2O2(aq) + 2H+(aq) + 2I–(aq) ⇒ I2(aq) + 2H2O(l)
- Use a large excess of H2O2 and I− - The change in [H2O2] and [I−] will be negligible ([H2O2] and [I−] are effectively constant) - So [H2O2] and [I−] will have no effect on rate of reaction
66
identify the RDS: Rate Equation: Rate = k[(CH3)3CBr] - Mechanism: - Step 1: (CH3)3CBr ⇒ (CH3)3C+ + Br− - Step 2: (CH3)3C+ + OH− ⇒ (CH3)3COH
- (CH3)3CBr must be in RDS or needed to form something in the RDS - Step 1 is RDS as there is One (CH3)3CBr in the rate equation
67
Identify the RDS: 2NO(g) + 2H2(g)⇒ N2(g) + 2H2O(g) - Rate Equation: Rate = k[NO]^2[H2] - Mechanism: - Step 1: NO + NO ⇒X - Step 2: X + H2 ⇒ Y - Step 3: Y + H2 ⇒ N2 + 2H2O
- 2 NO and 1 H2 must be in RDS or needed to form something in the RDS - Step 3 is RDS as two NO and one H2 are in the rate equation
68
What does the arrhenius equation show
For a chemical reaction the relationship between the rate constant, k, and the temperature, T
69
what is the arrhenius equation + units
70
what is the log version of the arrhenius equation
71
how can the arrhenius equation be used to plot a graph
The natural log form of the Arrhenius equation matches the equation for a straight line and it can be used to plot a graph from which the activation energy can be determined for a reaction.
72
draw a labelled graph of the arrhenius equation
- Gradient = negative Ea/R - Ea is always a positive number - Gradient x R = Ea
73
rearrange the natural form of the arrhenius equation for Ea
(lnA - lnk) x RT = Ea
74
rearrange the natural form of the arrhenius equation for T
T = (Ea / R x (lnA-lnk))
75
rearrange the natural form of the arrhenius equation for A
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