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A-Level Chemistry [OCR B Salters] (sorry for any spelling mistakes - there are many) > [Year 2] CI > Flashcards

Flashcards in [Year 2] CI Deck (47)
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1
Q

What might chemical companies consider in order to be as financially economical as possible?

A
  • Raw materials: cheaper, but must be widely available to ensure good sustainable supply.
  • Energy: required in manufacturing and transport, high TP increases costs. Purification of products also needs to be considered.
  • Waste: from by-products, due to gov regulations costs. Co-products can be sold off (although at a lower price).
  • High atom economic and percentage yields.
2
Q

What are the pros and cons of different reaction conditions that chemical companies consider?

A

Pressure:

  • Pros: beneficial to gas reactions, as high pressure speeds up the rate of reaction.
  • Cons: pumps, thicker pipes and vessels, and additional safety equipment are needed (which are expensive to run).

Catalysts:

  • Pros: allows reactions to run quickly at lower temps, saving money. Can be reused.
  • Cons: expensive, homogeneous catalyst must be separated after the reaction (additional step increases costs).

Temperature:

  • Pros: Higher temps = faster rate of reaction, more product per unit time.
  • Cons: More fuel needed, therefore more expensive.
3
Q

If you were to plot the Con - Time graph for both forward and backward reactions of a reversible reaction on the same graph, what would happen when they both plataue?

A
  • Dynamic equlimbrium is met.
  • This is where the rate (Con/Time) of forward reaction = rate of backwards.
  • At this point the concentrations remain constant.
  • ONLY occurs in a closed system.
4
Q

What effect does temperature have on Kc?

A
  • Only valid for one temperature.
  • Changing the temperature will change the equilibrium concentrations, and hence Kc will change too.
  • If temp change causes equilibrium to shift right, Kc INCREASES.
  • If temp change causes equilibrium to shift left, Kc
    DECREASES.
  • This can be explained using the Kc expression of a reaction.
5
Q

What effect does concentration have on Kc?

A

No effect

6
Q

What effect does a catalyst have on Kc?

A

No effect.

  • catalyst speed upi the rate of forward AND reverse reaction.
  • so speed up the rate at which equilibrium is established.
7
Q

What are the conditions of the Haber Process? And why?

A

Temp: 400ᵒC
∵ although it shifted the equilibrium to the left (as the forward reaction is exo), this is so the rate of reaction isn’t so small that it takes too long.

200atm
∵ although a high pressure would favour the forward reaction (due to moles), high pressures are expensive and can be dangerous.

For these reasons both of these are compromised.

8
Q

What are the advantages and disadvantages of the uses of chemical products?

A

Adv:

  • Parmaceutcals help prevent and cure disease.
  • Fertilisers ensure food is produced in the most efficient way possible
  • Plastics are widely used today.
  • Dyes and cleaning procus have helped improve living environment and lifestyle.

Dis:
- Some chemicals can be harmful to the environment.
(gases = air pollution) (liquid/solid = land pollution).
- Some chemicals are flamalble and explosive (must be stored and handled correctly.
- Some chemicals can be harmful to our health (via inhalation or contact).

9
Q

What is the Kc expression of 2A + B ⇌ 2C + D?

A

Kc = [C]²[D] / [A]²[B]

10
Q

How can we find out the concentrations of a substance without affecting the equilibrium?

A

Colourimetry:

  • Coloured solutions absorbs particular wavelengths of light.
  • This can be used to determine the absorption of the wavelength of light of the reaction at equilibrium.
  • A calibration curve of known concentrations can be plotted.
  • Our test sample is compared to these.

pH:

  • Useful if reactant and products have different pH values.
  • pH can be measured at equilibrium.
  • pH equation can then be used to calculate the concentration.
11
Q

How can you work out Kc from information about initial quantities and equilibrium?

A

Initial moles
Change in moles
Equilibrium moles

Equilibrium moles/vol = Equilibrium concentration

Kc = [products] / [reactants]

12
Q

What is the electron configuration of Nitrogen?

A

1s¹ 2s² 2p³

13
Q

Why is Nitrogen an unreactive gas at RTP?

A

Nitrogen is diatomic with triple covalent bonds which is required a lot of energy to break.

14
Q

How is ammonia made?

A

The Haber Process:
- the reaction between N₂ and H₂.

N₂ + 3H₂ ⇌ 2NH₃

15
Q

What is the significance of ammonia?

A
  • It shares 3 of its valence electrons with hydrogen and a lone pair of electron remains.
  • As a result it can form H-bonds with water, and so is very soluble.
  • It can also form dative covalent bonds using its lone pair of electrons (although these are not as strong as standard covalent bonds).
  • As a result of its lone pair, is also acts as a base to form ammonium ions (this N-H bonds is dative).
16
Q

List the oxides of nitrogens (and their properties)?

A
  • N₂O (Nitrogen(I) oxide/ Dinitrogen oxide): colourless gas with sweet smell.
  • NO (Nitrogen(II) oxide/ Nitrogen monoxide): colourless gas.
  • NO₂ (Nitrogen(IV) oxide/B Nitrogen dioxide): Brown gas with sharp, pungent smell.
17
Q

How do you test for ammonium compounds (and hydroxides)?

A

Litmus paper.

  • Add sodium hyrodxide
  • Heat, if ammonium is present amonia gas will be produced.
  • Use damp red litmus, this will turn blue as ammonia dissolves in the water.
18
Q

How do you test for Nitrate(V) ions?

A

Using sodium hydroxide and aluminium/ dervarda’s alloy.

  • add sodium hydroxide and aliminium foil/Devarda’s alloy to the solution you want to test.
  • Heat.
  • If nitrate(V) ions are present they are reduced by aluminium to ammonia gas.
  • Use damp red litmus, this will turn blue as ammonia dissolves in the water.
19
Q

What is the reaction that shows the production of Ammonia from Nitrogen gas?

A

N₂ + 3H₂ → 2NH₃

20
Q

What is the reaction that shows the production of Ammonium ions from Ammonia?

A

NH₃ + H⁺ → NH₄⁺

21
Q

What is the reaction that shows the production of Nirtate(III) ions from Ammonium ions?

A

NH₄⁺ + O₂ → NO₂⁻ + 4H⁺ + 2e⁻

22
Q

What is the reaction that shows the production of Nitrate(V) ions from Nirtate(III) ions?

A

NO₂⁻ + H₂O → NO₃⁻ + 2H⁺ + 2e⁻

23
Q

What is the reaction that shows the production of Nitrogen gas from Nitrate(V) ions?

A

2NO₃⁻ + 12H⁺ + 10e⁻ → N₂ + 6H₂O

24
Q

What are the reactions that shows the production of Nitrogen Oxides from Nitrogen gas?

A

N₂ + O₂ → 2NO
N₂ + 2O₂ → 2NO₂
2N₂ + O₂ → 2N₂O

25
Q

What is the definiton of the rate of reaction?

A

The change of concetration/ amount of a reactant or product, per unit time.

26
Q

What ways can be used to measure the rate of a reaction?

A

How long it takes for a precipitate to form:

  • Place cross on paper and time how long it takes for it to disappear.
  • Difficult to know when goes cloudy, use same observer to reduce error.

Mass lost:

  • If reaction produces gas, place on balance and measure the mass lost as gas is lost per unit time.
  • If gas is harmful or toxic must be done in a fume cupboard.

Volume produced:

  • Measure amount of gas produced in a gas syringe.
  • Done over a specified time.
  • Ensure syringe is correct size.

Change of pH:

  • Use pH meter to measure pH at regular intervals.
  • Plot graph, and use it to calc [H⁺].

Titrations:

  • take small samples at regular time intervals.
  • quench reaction
  • and titrate them against know con.

Colourimerty:

  • Coloured solutions absorbs particular wavelengths of light.
  • This can be used to determine the absorption of the wavelength of light of the reaction at equilibrium.
  • A calibration curve of known concentrations can be plotted.
  • Our test sample, at regular times, is compared to these.
27
Q

How might you slow a reaction down?

A
  • Dilution with dionised water.
  • Cool it down.
  • Add a chemical to stop the reaction (quenching)
28
Q

How can you find the rate from a graph?

A

Plot con - time graph.

Find gadient.

If not linear: draw a tangent at specific points and plot on a rate - time graph. The gradient of this is the total rate of reaction.

29
Q

What is a clock reaction?

A

A reaction wher you can time how long it takes for a reaction to occur.

30
Q

What assumptions are made when we do a clock reaction/Initial rates method and want to find its rate?

A
  • Temp remains constant.
  • [reactants] doesn’t change significantly during time period of the reaction.
  • Reaction hasn’t proceeded too far when the end point is observed.
31
Q

What does a quicker clock reaction mean for the rate?

A

Faster initial rate of reaction.

32
Q

Describe the Iodine clock experiment.

A

Equation: H₂O₂ (aq) + 2H⁺ (aq) + 2I⁻(aq) → H₂O (l) + I₂(aq)

  • Add sodium thiosulfate and starch (indicator) to excess Hydrogen peroxide.
  • Sodium thoisulfate reacts immediately with iodine produced in this reaction:

2S₂O₃²⁻(aq) + I₂ → 2I⁻(aq) + S₄O₆²⁻(aq)

  • When there is no more sodium tiosulfate left, I₂ reacts with starch.
  • This gives a deep blue/black colour.

∴ by varying the [I₂] and/or [H₂O₂] and keeping eveything else constant, the time take for blue/black colour change changes.

  • We can then work out the order of reaction.
33
Q

Describe the initial rates method (for finding out the order of reaction).

A
  • Find the rate of reaction for different concentrations over a set time period.
  • Work out the initial rates at each concentration.
  • Plot rate - concentration to work out orders.
34
Q

What are the different parts of a rate equation?

Rate = k[A]ᵃ[B]ᵇ

A

Rate = k[A]ᵃ[B]ᵇ

Rate = Rate/ moldm⁻³s⁻¹
k = rate constant/units vary
[A] = concentration of  A/ moldm⁻³
[B] = concentration of  B/ moldm⁻³
xᵃ = order with respects to a
xᵇ = order with repects to b
35
Q

What does the order of reaction tell us?

A

How the concentration of a substance affects the rate.

36
Q

Why does the rate constant increase when temperature does?

A
  • When temperture increases so doe the rate as moleulces have more kinetic energy
  • The concentration on substances remains the same.
  • Therefore for rate to increase so does k.
37
Q

What do different graphs look like for differing rates?

A

0 order:

  • linear concentration-time graph.
  • horizonle line rate-concentration graph.

1st order:

  • shallow curve concentration-time graph (changes by equal amounts).
  • linear rate-concentration graph.

2nd order:

  • steep curve concentration-time graph (changes by unequal amounts).
  • curved rate-contration graph.
38
Q

What is the half life of a reaction?

A

The time it takes for half of the reaction to be used up.

39
Q

How can half life be used to calculate the order of reaction?

A

0 order:
- decreasing half-life.

1st order:
- constant half-life.

2nd order:
- increasing half-life.

40
Q

How can half life be used to work out the rate constant?

A

k = ln2/t₀.₅

41
Q

What does the arrhenius equation link?

A

The activation energy and temperature to the rate constant(k).

42
Q

What is the Arrhenius equation?

A

k = Ae⁻ᴱᵃ/ᴿᵀ

k: Rate constant
A: Arrhenius constant
e: Universal constant
Ea: Activation energy / J
R: Gas constant
T: Temperature /K
43
Q

What relations can be derived from the Arrhenius equation?

A

k = Ae⁻ᴱᵃ/ᴿᵀ

  • As the activation energy (Ea) gets smaller, the rate constant (k) gets bigger: as many more particles have enough energy to react when they collide.
  • As temperature (T) increases, so does the rate constant (k): as particles have more kinetic energy, and are more likely to collide with at least the Ea.
44
Q

Express the Arrhenius equation in the form y = mx +c :

A
k = Ae⁻ᴱᵃ/ᴿᵀ
lnk = lnA - Ea/RT
lnk = -Ea/RT + lnA

y: lnk
m: -Ea/R
x: 1/T
c: lnA

45
Q

What reactants (or substances derived from them) must appear in the rate determining step?

A

Those that apear in the rate equation.

46
Q

Is the rate determining step fast or slow?

A

Slow.

47
Q

Deduce the rate equation using the following information…

Step 1: A + B → 2C (fast)
Step 2: 2C → D (slow)
Step 3: D + E → F + G (fast)
OVERALL: A + B + E → F + G

A

Rate = k[A][B][C]²

Reasoning:

  • C must be in the rate equation, as it is the rate-determining step.
  • [C] is raised to a power of 2 as two moles of it are used to make 1 mole of D in the rate-determining step.
  • A and B must also be in the rate equation as they make up C.