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Chemistry > C5 > Flashcards

C5 Flashcards

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1
Q

What is the yield?

A

The mass of a product made in a chemical process

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2
Q

What is theoretical yield?

A

The maximum mass it is possible to make from a given mass of reactants

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3
Q

How do you calculate theoretical yield?

A

Mass of limiting reactant
———————————— X sum of rfm of products
Total rfm of limiting reactant

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4
Q

How do you calculate percentage yield?

A

Actual yield
—————— X 100
theoretical yield

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5
Q

What affects the percentage yield?

A

The reaction may have reacted in a different way than expected
The reaction may not go to completion (often reversible reactions)
You may lose some of the product when you separate it from the reaction mixture and purify it

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6
Q

What is the atom economy?

A

Sum of rfm of desired product
—————————————— X 100
Sum of rfm of all products

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7
Q

What factors determine a reaction pathway/how you make a substance?

A

Yield of product
Atom economy
Usefulness of by-products
Rate of reaction
Equilibrium position (if it is a reversible reaction)

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8
Q

What are some uses of calcium chloride?

A

It’s an additive in concrete and polymers
Used to trap moisture in dehumidifiers

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9
Q

What is 1 litre in chemist terms?

A

1 cubic decimetre (dm^3)

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10
Q

What is 1ml in chemist terms?

A

1 cubic centimetre (cm^3)

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11
Q

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

A

Divide the cm^3 by 1000 to get 1000dm^3

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12
Q

What is concentration measured in?

A

g/dm^3

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13
Q

How do you calculate concentration?

A

Mass of solute (g)
———————————
Mass of solution (dm^3)

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14
Q

How do you calculate concentration in moles?

A

Amount of solute (mol)
————————————
Volume of solution (dm^3)

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15
Q

What is the formula to calculate the mol of a substance?

A

Mass of substance (g)
———————————————
Molar mass of substance (g/mol)

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16
Q

What is the titre in titration?

A

The difference between the initial burette reading and the final burette reading at the end-point.

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17
Q

How do make sure your titration is more accurate?

A

By repeating the titration until you obtain at least two concordant titres

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18
Q

What does concordant titre mean?

A

Titres that are within 0.1cm^3 of each other

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19
Q

What do you have to do to acquire a repeatable titre?

A

Swirl the flask during a titration to mix its contents.
(First titration gives rough idea of the titre)
In later reruns of the titration, quickly add acid to within a few cm^3 of the rough titre and the add the acid drop by drop.

20
Q

What is the molar volume?

A

One mole of any substance in the gas state occupies the same volume at the same temperature and pressure.

21
Q

What is the molar volume for 1 mole of gas at RTP (room temperature and pressure)

A

24dm^3/mol

22
Q

What is the rate of reaction?

A

It is a measure of how quickly reactants are used or products are formed

23
Q

What are the formulae for the rate of reaction?

A

Amount of reactant used / amount of products formed
——————————————————————————
Time taken

24
Q

What apparatus would you use to measure the volume of a gas?

A

A gas syringe

25
Q

How does a gas syringe work?

A

As the syringe fills, the plunger moves outwards and you can record the volume of gas it contains.

26
Q

What is the instantaneous rate of reaction?

A

The rate of reaction at a particular time

27
Q

What are the conditions for a reaction to occur?

A

The reactant particles collide with each other
The colliding particles have enough energy to react

28
Q

What is a successful collision?

A

When reactant particles collide with each other and the particles have energy equal to or higher than the activation energy, making a successful reaction.

29
Q

Why do reactions go faster at higher temperature?

A

The particles move more quickly and collide more often
A greater proportion of the colliding particles have the activation energy or more

30
Q

How is reaction time related to the rate of reaction?

A

The rate of reaction is inversely proportional to the reaction time

31
Q

Why do reactions fo faster at higher concentrations?

A

The particles become more crowded so they collide more often

32
Q

How is the product of a reaction related to the limiting reactant?

A

The amount of product is proportional to the liming reactant

33
Q

What is a catalyst?

A

A substance that increases the rate of reaction without being used up in a reaction. Certain catalysts are used in certain reactions

34
Q

What is a biological catalyst (enzymes)?

A

Enzymes are proteins that act in biological systems. Different enzymes catalyse different reactions.

35
Q

How do catalysts work?

A

They lower the activation energy
A greater proportion of the colliding particles have the activation energy or more
The rate of successful collisions increases

36
Q

Why do reactions go faster with powders?

A

More particles are available for collisions
Collisions are more likely so particles collide often

This is due to the higher surface area to volume ratio

37
Q

What is a reversible reaction?

A

A reaction in which the products can react together to form the original reactants

38
Q

What is dynamic equilibrium?

A

When the rates of forward reaction and the backward reaction become equal (only happens in a close system)

39
Q

What happens during equilibrium position?

A

The concentrations of all the reacting substances remain constant

40
Q

How does concentration affect equilibrium position?

A

If the concentration of a substance is increased, the equilibrium position moves in the direction away from that substance

41
Q

What happens to the equilibrium position when you change the pressure in a reversible reaction?

A

The equilibrium position would move in the direction of the fewest moles of gas

42
Q

What happens to the equilibrium position when you increase the temperature?

A

When you increase the temperature, the equilibrium position moves towards the direction of endothermic change

43
Q

What is Le Châtelier’s principle?

A

“When a change is made to a reaction at equilibrium, the position of equilibrium moves to oppose the change”

44
Q

What does negative delta (triangle) H mean in a reaction?

A

The reaction is exothermic

45
Q

What does a positive delta (triangle) H means in a reaction?

A

The reaction is endothermic

46
Q

What are compromise conditions?

A

When you need a high conditions for a higher yield but you can’t kill the enzymes/it can’t be too expensive/ it can’t be too hazardous

Chemistry (8 decks)

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