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Chemistry A-level ♡ > kinetics. > Flashcards

kinetics. Flashcards

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1
Q

What is collision theory?

A

The idea is that for a chemical reaction to occur, particles must collide with energy greater than or equal to the activation energy and in the correct orientation.

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2
Q

What is an ineffective collision?

A

When particles collide in the wrong orientation or when they don’t have enough energy and bounce off each other without causing a chemical reaction.

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3
Q

What is a successful collision?

A

When particles collide with sufficient energy to results in a reaction. (and orientation).

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4
Q

What is collision frequency and how does this relate to reaction rate?

A

The collision frequency is the number of collisions per unit of time. when more collisions take place per unit of time, the number of particles with energy greater than or equal to the activation energy increases. this leads to more successful collisions and an increase in the rate of reaction.

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5
Q

What is the Activation energy?

A

For a reaction to take place, the reactant particles need to overcome a minimum amount of energy. this energy value is called the activation energy.

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6
Q

What is an Exothermic reaction?

A

A reaction where the enthalpy (energy change) of the teaching system decreases. the enthalpy change is negative and energy is transferred from the reacting system to the surroundings.

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7
Q

What is an Endothermic reaction?

A

A reaction where the enthalpy of the reacting system increases. the enthalpy change is positive and energy is transferred to the reacting system from the surroundings.

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8
Q

What is an enthalpy profile diagram?

A

A diagram where the change in reaction enthalpy can be detailed.

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9
Q

How does Increasing temperature affect the rate of reaction?

A

increasing temperature increases the kinetic energy of particles. this increases the frequency of collisions and a greater proportion of collisions will succeed the activation energy and have enough energy needed to react. this gives more successful collisions.

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10
Q

How does increasing the concentration of a solution affect the rate of reaction?

A

increasing the concentration increases the rate of reaction as there are a greater number of particles available to react. therefore the frequency of collisions increases and so there is a higher proportion of successful collisions.

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11
Q

How does increasing the pressure of gases in a reaction affect the rate of reaction?

A
  1. Increasing the pressure of a reaction involving gases forces the gas particles closer together. this will increase the frequency of particle collisions and therefore successful collisions and will increase the rate of reaction.
  2. When adding more of the gas to increase the pressure, there are a greater number of particles available to react. therefore the frequency of collisions increases and so there is a higher proportion of successful collisions.
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12
Q

How does increasing the surface area of a solid affect the rate of reaction?

A

increasing the surface area of solid reactants increases the number of particles that are exposed and available to react and as a consequence this increases the frequency of particle collisions and successful collisions, increasing the rate of reaction.

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13
Q

How does using a catalyst affect the rate of reaction?

A

Using a catalyst provides an alternative route for the reaction, with a lower activation energy. this means that particle collisions need less energy for a reaction to occur and more particles have enough energy to succeed the activation energy and react, increasing the rate of reaction.

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14
Q

What is Maxwell- Boltzmann distribution?

A

a graph that shows the number of particles and distribution of their energies at a certain temperature.

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15
Q

Where is the most probable energy of particles on a M-B distribution graph?

A

usually the peak of the curve.

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16
Q

Where is the mean energy of particles on a M-B distribution graph?

A

to the right of the peak of the curve.

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17
Q

What does the area under the curve of the M-B distribution represent?

A

number of particles.

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18
Q

Why does the M-B graph start at the origin?

A

because no particles have zero energy

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19
Q

Why doesn’t the M-B graph touch the x-axis?

A

because there is no upper limit to the energy of particles/

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20
Q

How does increasing the temperature affect the M-B distribution graph?

A

At higher temperatures, the curve flattens and shifts to the right. however the area under the curve stays the same due to the same number of particles being present.

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21
Q

How does decreasing the temperature affect the M-B distribution graph?

A

At lower temperatures, the cure steepens and has a high peak to the left of the graph. the area under the curve remains the same.

22
Q

Why does increasing the temperature by a small amount have a large effect on the rate of reaction? (use the Maxwell-Boltzman distribution diagram)

A

At higher temperatures, there are more reactant molecules to the right of the graph with higher energies, this leads to a higher proportion of molecules with energy greater than the activation energy meaning more particles can have successful collisions.

23
Q

What is the rate of reaction?

A

the change in the concentration of a substance per unit time. It can be calculated using: a change in the amount of reactant or product (moldm^3/ time(s)

24
Q

how do you find the rate of reaction at a point in time using a concentration-time graph?

A
  1. draw a tangent to the curve at the specific point you want to work out.
  2. calculate the gradient of the tangent by doing change over y/ change over x/
  3. don’t forget to put in units of moldm^3!!
25
Q

What would happen to the graph showing the volume of a product being produced over time if we increased the temperature of the reactants?

A
  1. the volume of products produced remains the same so the line ends at the same point
  2. however the line is steeper because the reaction produces the products at a faster rate
26
Q

What would happen to the graph showing the volume of a product being produced over time if we halved the concentrations of the reactants?

A
  1. the reaction produces the same volume of the products so the rate is the same.
  2. the line would be half as tall as the original as only half the amount of product can be formed.
27
Q

What would happen to the graph showing the volume of a product being produced over time if we increased the surface area of the reactants?

A
  1. The graph line would be much steeper as more area for reactants to happen
  2. graph line plateaus quicker as the reaction occurs faster
28
Q

What practical is used to measure the rate of reaction by using a continuous monitoring method?

A

Investigation of how the rate of the reaction with magnesium and HCl changes over time. while keeping the temperature constant. used to investigate the effect of varying the concentration of the acid on the rate of reaction.

29
Q

What is the magnesium and HCl experiment?

A
  1. measure 50cm^3 of HCL in a measuring cylinder using a funnel to be safe. and pour into the conical flask
  2. the conical flask must be connected to an arm connected to a gas string that will measure the volume of hydrogen gas produced.
  3. place in a piece of magnesium and at the same time put the bung in and start the clock
  4. every 15 seconds record the volume of hydrogen gas produced for 150 seconds.
  5. repeat at a different concentration
30
Q

How does changing the concentration affect the Maxwell-Boltzmann distribution graph?

A
  1. The shape of the curve remains the same
  2. higher /lower depending if the pressure is increased or decreased.
31
Q

What is a catalyst?

A

A catalyst is a substance that speeds up the rate of reaction but is chemically unchanged at the end.

32
Q

How does a catalyst increase the rate of reaction?

A

provides the reactants with an alternative reaction pathway which is lower in activation energy than the uncatalysed reaction.

33
Q

What are enzymes?

A

biological catalysts.

34
Q

What are homogenous catalysts?

A

where the catalyst is in the same phase (state of matter) as the reactants like enzyme reactions with organisms in an aqueous solution

35
Q

What are heterogeneous catalysts?

A

where the catalyst is in a different phase than the reactants. like a liquid or gas working upon the surface of a solid.

36
Q

Why do we use catalysts?

A
  1. Allow reactions to take place at lower temperatures decreasing energy costs
  2. enable different reactions to be used with better atom economy reducing waste
  3. are often enzymes generating specific products
  4. can reduce pollution i.e. use of catalytic converters.
37
Q

Do catalysts affect the enthalpy change on a reaction profile diagram?

A

No, they only lower the activation energy, the enthalpy change remains the same.

38
Q

Using a Maxwell Boltzmann diagram how do catalysts speed up the rate of reaction?

A

by lowering the activation energy a higher proportion of particles are to the right of the activation energy meaning more successful collisions.

39
Q

What is the disappearing cross experiment?

A

A reaction between sodium thiosulphate and HCL shows how concentration affects the rate of reaction and temperature. makes an insoluble sulfur precipitate this experiment is an approximation of the rofr because it does not include concentration.

40
Q

What happens in the disappearing cross experiment?

A
  1. measure 50 cm^3 of sodium thiosulfate and 10C^3 of HCl
  2. acclimatize both in a water bath for 2 minutes
  3. place a black marked cross under a conical flask
  4. add in both sodium thiosulfate and HCL and immediately start the timer
  5. record the time taken for the cross to disappear while the precipitate forms
  6. repeat at different temperatures.
41
Q

What is the symbol equation for the sodium thiosulfate and HCL reaction?

A

Na2S2O3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + SO2(g) + S(s)

42
Q

What else could be used instead of the human eye when determining when the precipitate is fully formed?

A

A light sensor was placed under the flask and linked to a computer. this removes human error.

43
Q

What must you consider when doing the disappearing cross experiment?

A
  1. the temperature of the reaction mixture will change as the reaction proceeds so we need to calculate the average temperature (using start and end temperatures) or place the bath in a thermostatically controlled water bath or electric water bath.
  2. sulfur dioxide is a gas that aggravates asthmatics, so we must use a fume cupboard to pour the finished reaction into the fume cupboard sink
44
Q

What is uncertainty?

A

an estimate attached to a measurement which is used to characterise the range of values the true value could lie. this is characterised by +- x

45
Q

What is experimental error?

A

the difference between the measurement and the true value. or the difference between two values.

46
Q

how do you calculate uncertainty?

A

Half a division on either side of the smallest unit on the scale. Or half the smallest division.

47
Q

How to use a burette?

A
  1. record figures that are known for certain
  2. read to half a division
  3. record values to 2 decimal places ending with a 0 or a 5.
  4. aim for concordant results
48
Q

How to combine errors using a burette?

A

when using a burette we are measuring the change in volume, this means there will be an error in both our second and first reading. so we combine the errors (+-0.05 initial ) +(+-0.05) = ).1 uncertainty.

49
Q

What is accuracy?

A

this measures how close a measured value is to its true or accepted value.

50
Q

What is precision?

A

This measures how closely two or more measurements agree with each other

51
Q

What is the percentage uncertainty?

A

percentage uncertainty = percentage / reading x 100

52
Q

How to calculate Experimental error?

A

Experimental error = real answer - experimental answer / real answer x 100.

53
Q

how would you use the experimental error to determine the accuracy of a set of results?

A

If the experimental error is smaller than the total apparatus error then you have an accurate result.
if the experimental error is bigger than the total apparatus error you have an inaccurate result.

54
Q
A

Chemistry A-level ♡ (4 decks)

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