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Chemistry > Kinetics > Flashcards

Kinetics Flashcards

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1
Q

When can reactions occur

A

Only when collisions take place between parties having sufficient energy and correct orientation

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2
Q

What is this sufficient energy called

A

The activation energy

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3
Q

Activation energy

A

The minimum energy required to start a reaction by breaking of bonds

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4
Q

Why do most collisions not lead to a reaction

A
  • may be insufficient energy

- orientation may be incorrect

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5
Q

Rate of reaction

A

The change in concentration of a substance in a given time

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6
Q

What are the units of rate

A

mol dm-3 s-1

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7
Q

Why does the rate decrease as the reaction proceeds

A

The concentration of reactant falls

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8
Q

What is the rate at a particular time equal to

A

The gradient at that time

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9
Q

What is the correlation between concentration and rate

A

Increasing the concentration increases the rate

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10
Q

Why does increasing concentration increase rate

A
  • more particles per unit volume
  • more collisions per second
  • faster rate
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11
Q

What is the correlation between pressure of gases and rate

A

Increasing the pressure increases the rate

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12
Q

Why does increasing pressure gases increase rate

A
  • more particles per unit volume
  • more collisions per second
  • faster rate
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13
Q

What is the correlation between increasing SA of solids and rate

A

Increasing SA increases rate

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14
Q

Why does increasing SA of solids increase rate

A
  • more surface of solid exposed to other reactant
  • more collisions per second
  • rate is faster
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15
Q

What is correlation between temperature and rate of reaction

A

Increasing temperature increases the rate

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16
Q

Why does increasing temperature increase rate

A
  • more particles have energy equal to or greater than activation energy
  • more successful collisions
  • rate is faster
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17
Q

What does adding a catalyst do to rate of reaction

A

Increases it without it being used up

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18
Q

Why does adding a catalyst increase rate of reaction

A
  • provides alternate pathway
  • lower activation energy
  • more successful collisions
  • faster rate
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19
Q

Experiment between HCl and CaCO3 to show effect of conc on RoR

A

Add CaCO3 to HCl

Collect CO2 produced in a gas syringe

Record volume of CO2 at regular intervals

Produce graph of volume of CO2 against time

20
Q

What would a curve look like with same number of moles of acid but higher concentration

A

Steeper curve but levels of at same volume of CO2

21
Q

What would curve look like with half moles acid but same conc

A

Same steepness of curve but half final volume of CO2

22
Q

What does the reaction between sodium thiosulfate and hydrochloric acid produce

A

A precipitate of sulfur, sodium chloride and sulfur dioxide

23
Q

How can the rate of reaction between sodium sodium thiosulfate and hydrochloric acid be monitored

A

Measure time taken for cross to disappear from view

Cross obscured by PPT of sulfur

24
Q

What is measuring time taken for cross to disappear called

A

Initial rate method

25
Q

How can temp be known as accurately as possible in reaction between sodium thiosulfate and hydrochloric acid

A

Measure initial and final temp- take and use an average

26
Q

What could be used to prevent SO2 escaping from the reaction

A

Put a lid on the reaction vessel to minimise escape of CO2

27
Q

Why is a STOP bath used in reaction between sodium thiosulfate and hydrochloric acid

A

Both acid and sulfur dioxide can be neutralised

28
Q

What is the independent variable in the reaction between sodium thiosulfate and hydrochloric acid

A

Temperature

29
Q

What is the dependent variable in the reaction between sodium thiosulfate and hydrochloric acid

A

Time

30
Q

Why is the hazard associated with sulfur dioxide in this investigation considered to be low

A

Amount of SO2 low because solutions are dilute

SO2 is soluble- doesn’t all escape as a gas

31
Q

Why do the particles in a particular sample have a spread of energies when the samples collide

A

Energy is exchanged between them

32
Q

What does the Maxwell-Boltzmann distribution show

A

The distribution of energies of the particles within a sample

33
Q

What is the important feature of the maxwell boltzmann distribution that is seen at the origin of the graph

A

No particles have no energy

34
Q

What is the important feature of the maxwell boltzmann distribution that is seen at the end of the graph

A

The curve doesn’t meet back with the x axis- no maximum energy

35
Q

What is the important feature of the maxwell boltzmann distribution at the highest point of the graph

A

The most likely every is not very high

36
Q

What does the shaded area represent on a maxwell Boltzmann distribution

A

Particles which will successfully collide

37
Q

How is the peak on a maxwell distribution curve at a higher temperature different

A

It’s lower and to the right

38
Q

What is the difference between most probable energy in a maxwell Boltzmann distribution curve at a higher temp

A

The most probable energy is higher

39
Q

What is the change in area under the curve maxwell botlzmann at higher temp

A

Area under curve remains same

40
Q

How is the shaded area different in maxwell Boltzmann curve at higher temp

A

Shaded area now much larger as far more particles have energy equal to or greater than activation energy

41
Q

Why does a small temperature increase lead to a large increase in rate

A

Far more particles will now have energy greater than or equal to activation energy so far more successful collisions

42
Q

What is a catalyst

A

A substance which increases the rate of a chemical reaction without being changed in chemical composition or amount

43
Q

What does a catalyst provide

A

An alternative reaction route with a lower activation energy

44
Q

What is lowered and what is unchanged in the presence of a catalyst

A

Activation energy lowered but enthalpy not changed

45
Q

What does a maxwell Boltzmann distribution look like with a catalyst

A

Shaded area is bigger so more molecules have energy greater than or equal to activation energy

More collisions are successful so rate of reaction increases

Chemistry (42 decks)

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