Chemistry Rate Of Reaction Unit Flashcards

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1
Q

What must happen for a reaction to be successful?

COLLISION THEORY

A

-For a reaction to be successful reactant particles MUST collide with the correct orientation and have energy greater than the activation energy

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2
Q

What must happen to speed up a reaction?

A

-To speed up a chemical reaction you must increase the frequency of successful collisions

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3
Q

Define activation energy.

A

-Activation energy is the minimum amount of energy required for a reaction to take place and successful collisions to occur

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4
Q

What happens when activation energy is higher?

A

-If it is higher, fewer collisions will have the energy required so the reaction will occur more slowly

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5
Q

Define reaction rate.

A

-Reaction rate is defined as the amount of reactant used up or the amount of product produced in a given amount of time

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6
Q

What are the four conditions that affect the rate of reaction?

A

-Presence of a catalyst
-Surface area
-Temperature
-Concentration

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7
Q

Why do scientist need to understand rates of reaction?

A

-Safety (how much gas or heat might be released in a short space of time)
-Medicines (how much is required for a therapeutic effect to avoid negative effects)
-Profit per unit of time (when making a substance for sale)

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8
Q

Define catalyst.

A

A catalyst is a substance which speeds up a chemical reaction by lowering the activation energy, remaining unchanged by the reaction

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9
Q

How does surface area affect rate of reaction?

A

-If we increase the surface area of a solid reactant, more reactant particles are exposed to each other, leading to an increase of the frequency of collisions (and hence the frequency of successful collisions
-This means that an increase in surface area results in a higher reaction rate

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10
Q

How does temperature affect the rate of reaction?

A

If we increase the temperature:
1. The reactant particles will have more kinetic energy, and so
2. More particles will have sufficient energy to form products, and
3. Therefore the frequency of successful collisions (and hence reaction rate) increases

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11
Q

What is the unit for concentration?

A

molL^-1

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12
Q

How does concentration affect the rate of reaction?

A

Increasing the concentration means:
1. There are more reactant particles in a given volume of space, so
2. particles collide more frequently, so
3. successful collisions happen more frequently, increasing reaction rate

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13
Q

How do we measure rate of reaction?

A
  1. Measure the volume of gas produced over time
  2. Measure how long it takes for a colour change to occur (opaque)
  3. Time how long it takes for a reactant to react away (disappear)
  4. Record the mass lost form a reaction over time

All of these methods involve time as a crucial aspect.

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14
Q

Define exothermic reaction.

A

Exothermic reactions are reactions that give out heat (release) heat energy to the surroundings.

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15
Q

Define endothermic reaction.

A

Endothermic reactions are reactions that take in (absorb) energy from the surroundings
-Energy is transferred as heat energy from the surroundings into the reaction

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16
Q

How do you calculate the activation energy?

A

Peak-reactants

17
Q

How do you start any reaction?

A

You must break the bonds of the reactants

18
Q

What does the arrow between the reactants and the products mean?

A

The loss or gaining of chemical energy in the reaction

19
Q

How do you calculate the overall energy change?

A

Products-reactants (doesn’t matter if the answer is negative)
-Exothermic will be negative
-Endothermic with be positive

20
Q

Do catalysts change the overall energy change?

A

No, the difference between the reactants and products remains the same, only the activation energy, which has decreased, is different

21
Q

What does the S.A.M.E acronym stand for?

A

Subjectivity: Did the practical involve any aspect which was down to human judgement?
Amounts: Were the same amounts of all of the control reagents used in each experiment?
Methods: Was the method exactly the same every time?
Equipment: Was the equipment used in each experiment?

22
Q

Subjectivity

A

-Consider the experiments where you had to read the volume of gas from the measuring cylinder…

-During the experiment, the gas was constantly being produced. That made the scale hard to read and so you could mention this in your evaluation.

-This tells the reader that whilst your results were gathered to the best of your ability, they are not without human error.

-Repeating an experiment will reduce the effect of subjectivity and make results more reliable.

23
Q

Amounts

A

Amounts usually refers to the controlled variables, but can refer to any aspect of reagents used in an experiment.

-When we investigated temperature we had to make sure surface area was the same. Was it? Did you make sure the surface area of the marble was kept the same? Probably no - so you need to mention this in your evaluation.

-The trend of your results will still be the same with ‘approximate’ amounts BUT if you were to repat it then it is unlikely that you would get exactly the same values

-This impacts repeatability (similarity of results obtained by the same person on the same day) and reproducibility (similarity of results obtained by different people on different days).

-Repeating an experiment will reduce the effect of natural variation and make results more reliable

24
Q

Method

A

-So far, when investigating rate we have had two methods of collecting results; collecting gas produced over time and tracking mass loss over time.

-Can we compare these results? How do we know whether 2 g/s represents a faster rate than 30cm^3/s?
If you used a different method are your results comparable?
This is an extreme case but even small changes to the method can impact results. This becomes more likely when someone else is trying to reproduce an experiment

25
Q

Equipment

A

The use of equipment can have a large effect on how PRECISE our data can be (how many decimal places on a balance? How precisely can we measure temperature on a 100C vs 50C thermometer?) and how ACCURATE our result is.

Choice of equipment needs to be appropriate for the needs of the experiment:
-If our measurements are not very precise then we can get lots of RANDOM ERROR occurring
-The wrong equipment can also cause SYSTEMATIC ERROR causing results to be invalid

26
Q

What happens when activation energy is lower?

A

-If it is lower, more collisions will occur with the required energy so the reaction will occur more quickly

27
Q

How does surface area affect rate of reaction?

A

-If we increase the surface area of a solid reactant, more reactant particles are exposed to each other, leading to an increase of the frequency of collisions (and hence the frequency of successful collisions
-This means that an increase in surface area results in a higher reaction rate

28
Q

How does temperature affect the rate of reaction?

A

If we increase the temperature:
1. The reactant particles will have more kinetic energy, and so
2. More particles will have sufficient energy to form products, and
3. Therefore the frequency of successful collisions (and hence reaction rate) increases

29
Q

How does concentration affect the rate of reaction?

A

Increasing the concentration means:
1. There are more reactant particles in a given volume of space, so
2. particles collide more frequently, so
3. successful collisions happen more frequently, increasing reaction rate

30
Q

How does the presence of a catalyst affect the rate of reaction?

A

-When a catalyst is present, the rate of reaction increases because the catalyst lowers the activation energy so more collisions will occur with enough energy (energy greater or equal to the activation energy) to react, so the reaction will occur faster (and hence the frequency of successful collisions increases)

31
Q

What does room temperature mean for chemical reactions?

A

The activation energy will be much lower

32
Q

What does a negative energy change mean?

A

There is a loss of energy from the system, so the reaction is exothermic.

33
Q

What does a positive energy change mean?

A

There is a gain in energy in the system and the reaction in endothermic.

34
Q

What should a graph title be?

A

A graph to show the effect of changing the (IV) on the (DV)

35
Q

How should an aim be written?

A

To determine the effect of changing the (IV) on the (DV) when (context)

36
Q
A