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CHEMISTRY > C5 - Monitoring and Controlling Chemical Reactions > Flashcards

C5 - Monitoring and Controlling Chemical Reactions Flashcards

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1
Q

What is concentration?

A

Refers to how much particules there are in a fixed volume

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2
Q

Equations for concentration:

A

Concentration (mol/dm^3) = moles / volume (dm^3)

or

Concentration (g/dm^3) = mass / volume (dm^3)

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3
Q

How do you convert from cm^3 to dm^3?

A

Divide by 1000

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4
Q

What are titrations used to find?

A

To find exactly how much acid is needed to neutralise a given quantity alkali

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5
Q

Titration experiment steps:

A

1) Fill a clean, dry burette with acid
2) Note the starting volume of acid in the burette
3) In a clean, dry pipette transfer 25cm^3 of an alkali in conical flask
4) Add a few drops of indicator to the alkali in flask
5) While swirling regularly, slowly add the acid to the alkali
6) The indicator changes colour when all alkali has been neutralised - then stop adding the acid to the alkali
7) Record the volume of acid used to neutralise the alkali (the titre)
8) Repeat three more times and calculate the mean.

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6
Q

What is the molar volume?

A

The volume occupied by one mole of gas

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7
Q

General equation for molar volume:

A

Molar volume (dm^3/mol) = gas volume (dm^3) / number of moles

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8
Q

What is the molar volume always in room temperature and pressure?

A

24dm^3/mol

-One mole of any gas at RTP (Room temperature or pressure) occupies 24dm^3 of space

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9
Q

Equation for molar volume at RTP?

A

Volume of gas (dm^3) = 24dm^3/mol x Moles

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10
Q

What is the percentage yield?

A

A percentage shows the overall success of the experiment compares what we expected to get (theoretical yield) and what we actual got (actual yield).

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11
Q

Why is it hard to get 100% percentage yield?

A

Products can be lost by:

  • Filtration
  • Evaporation
  • Transferring liquids
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12
Q

What is the actual yield and theoretical yield?

A

Actual yield: The actual mass of products that were converted from reactants

Theoretical yield: The mass of products if all of the reactants had converted

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13
Q

Equation for percentage yield:

A 
Percentage yield(%) = 
(actual yield / theoretical yield) x 100
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14
Q

What is atom economy?

A

Is the percentage of reactants changed to useful products

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15
Q

Atom economy Equation?

A

Atom economy (%) = (Total Mr of desired products / total Mr of all Products) x 100

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16
Q

Why is high atom economy beneficial?

A
  • It is beneficial for profits and environment
    1) High atom economy makes these reactions sustainable (the don’t waste loads and produce lots of desired products so it doesn’t run out quickly)
    2) They are profitable (not lots of waste products). Raw materials are expensive to buy and rid of waste.
17
Q

What are factors considered in industry?

A
  • Atom economy
  • The percentage yield
  • The rate of reaction. The rate of reaction must be fast enough to produce the amount of product you need in a sensible amount of time
  • Whether the reaction is reversible. To keep the yield of a reversible reaction high, you might need to alter the reaction conditions, and doing this can be expensive.
18
Q

What is the rate of reaction?

A

The measure if how fast the reaction happens

19
Q

Mean rate of reaction equation:

A

Rate of reaction = amount of product formed / time

20
Q

What experiment to follow to find rate of reaction using precipitation?

A

-Use sodium thiosulphate and hydrochloric acid

1) Put a flask with thiosulphate in it on a piece of paper with a cross on it
2) Add hydrochloric acid and start stopwatch
3) Mix the two reactants
4) Observe how the long it takes for the cross to become obscure to see as a precipitate of sulphur. When you cannot see the cross anymore stop the stopwatch and that is the rate of reaction.

21
Q

What experiment to follow to find rate of reaction using change in mass?

A

1) Use a mass balance to see how much gas is produced and how quickly
2) Use a cotton wool as it lets gases escape but not solids, liquids or aqueous out.
3) As gas is produced from reaction, the lost mass is easily measured on the balance. The quicker the mass is lost the faster the rate of reaction

22
Q

What experiment to follow to find rate of reaction using the amount of gas given off?

A

1) Involves using a gas syringe to measure volume given off

2) The more gas given off in a set time, the higher the rate of reaction

23
Q

What is the experiment to show how surface area affects rate of reaction?

A

-Reaction of Hydrochloric acid and marble chip

1) Set up apparatus (flask and gas syringe)
2) Measure the volume of gas produced using a gas syringe in a specific amount of time
3) Do for large chips, small chips, powdered chalk and double quantity of small chips

24
Q

Expected results for the experiment showing how surface area affects the rate of reaction?

A

1) smaller chips means they have a higher surface area
2) The whole experiment shows how the smaller the object (higher surface area) leads to higher rate of reaction

3) The order of fastest rate of reaction to slowest ->
- DOUBLE QUANTITY OF SMALL CHIPS : Shows adding more chips, extra surface area and increases rate of reaction
- Then, POWDERED CHALK: smallest solid
- Then SMALL CHIP, next smallest solid
- LARGE CHIP, largest and has slowest rate of reaction

25
Q

How do we know rate of reaction on graph?

A
  • The reaction has stopped when the line flatterns (rate of reaction is the amount of time for the reaction to finish)
  • The steeper the gradient the faster the reaction is (high amounts of product formed in short amount of time)
26
Q

How do you find the gradient of a curve?

A
  • A curve means the rate of reaction changes at different points
  • To find gradient of a certain point, draw a tangent to the curve at that point
  • Find the gradient of the tangent
27
Q

Equation for working out rate of reaction?

A

Rate of reaction = 1 / time

Rate of reaction indirectly proportional to time.
As time increases = rate of reaction decreases
As time decreases = rate of reaction increases

EG. If a reaction takes 86 seconds to stop, the rate of reaction will be 1/86.

28
Q

What is the collision theory?

A
  • Reactions occur when particles collide with each other with enough energy.
  • The more frequent the collision, the higher the rate of reaction
29
Q

Factors affecting the rate of reaction?

A

1) Volume
2) Concentration
3) Temperature
4) Surface area (size of particles)

30
Q

How does volume affect the rate of reaction?

A
  • When volume is decreased, particles have less space, leading to more frequent collision, higher rate of reaction
  • When volume increased, particles have more space, less frequent collision, lower rate of reactions
31
Q

How does concentartion affect the rate of reaction?

A
  • Higher concentration, particles more crowded, more frequent collisions, higher rate of reaction
  • Lower concentration, particles less crowded, less frequent collisions, lower rate of reaction
32
Q

How does Temperature affect the rate of reaction?

A
  • Higher rate of reaction, particles have more kinetic energy, more frequent collisions with more force, rate of reaction increase
  • Lower rate of reaction, particles have less kinetic energy, less frequent collisions, lower rate of reaction
33
Q

How does size of particles affect the rate of reaction?

A
  • Decreasing particle size there is more surface area the collision can take place on, higher rate of reaction
  • increasing particle size there is less surface area the collision can take place on, lower rate of reaction
34
Q

What are catalysts?

A

A substance that increases the rate of reactions without being chemically changed or used up in the end

35
Q

How do catalyst work?

A

They lower the activation energy (the energy required for a chemical reaction to start) by providing a alternate route for reaction to follow which has a lower activation energy

36
Q

What is the relationship between concentration and rate of reaction?

A

Directly proportional: HIgher the concentration the higher the rate of reaction

37
Q

What is the relationship between concentration and time?

A

Indirectly proportional: Higher the concentration the less time for reaction to stop

CHEMISTRY (7 decks)

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