Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry A2 UNIT 4 > Kinetics and Equilibria > Flashcards

Kinetics and Equilibria Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What is the rate of reaction?

A

The change in the amount of reacts or products in a given time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the difference to rate of reaction when the reactants are in solution?

A

the rate will be change of concentration per second and the units will be moldm-3.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do you find the rate of reaction from a graph?

A

Graph of reactant/product against time for a reaction the rate at any point is given by the gradient at that point on the graph. If the graphs a curve, you have to draw a tangent to the curve and find the gradient of that.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the rate equation for A+B=C+D

A

Rate=k[A]^m[B]^n square brackets show conc. UNITS- moldm^-3s^-1 k= rate constant m and n are orders of reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do reaction orders show?

A

How the conc. of the reactant affects the rate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

If [A] changes and the rate stays the same what is the order of reaction with respect to A?

A

0 so if [A] doubles or triples the rate will stay the same.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

If the rate is proportional to [A], what will the order of reaction be in respect to A?

A

1 If [A] doubles, the rate will double. If [A] triples, the rate will triple

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

If the rate is proportional to to [A]^2, what will the order of reaction be?

A

2 So if [A] double, the rate will be 2^2=4 times faster. If [A} triples, the rate will be 3^2 =9 times faster.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the overall order of reaction?

A

m+n

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the rate constant and how does it affect the same for a certain reaction?

A

k is the rate constant- the bigger it is, the faster the reaction. The rate constant is always the same for a certain reaction at a certain temperature. BUT if you increase the temperature, the rate constant rises too.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When you increase the temperature of a reaction what changes and causes this?

A

Rate of reaction increases, the conc. of reactants and the orders of reaction don’t change . Must be increase in the value of k that has cause increase.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the initial rate of reaction?

A

The rate right at the start of the reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do you find the initial rate of reaction from conc.-time graph?

A

Collect data by setting up a reaction and then monitoring the amount of a reactant over time. The amount of reactant decreases with time because it gets used up in the reaction. Once the reaction is complete, plotting the concentration of reactant against time gives a conc. time graph. Calculate gradient at time=0. Draw tangent to curve at time=0 and draw in horiz. and vert. lines to make a triangle with the tangent as its longest side. Horiz. / Vertical.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do you use the initial rates method to work out order of reaction for each reactant?

A

1: Set up a reaction and monitor amount of reactant/product over time. 2: Repeat the experiment several times using different initial concentrations of reactants. You should usually only change one of the concs. at a time, keeping the rest constant. 3: Calculate initial rate for each experiment. 4: Finally, see how the initial conc. affect the initial rates and figure out what order for each reactant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the rate determining step?

A

Each step of a reaction can have a different rate. The overall rate is determined by the step with the slowest rate- rate determining step.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you know if a reactant is involved in the rate determining step?

A

If a reactant is in the rate equation it must affect the rate. If not in rate equation it is not involved in rate determining step- neither is anything derived from it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does the order of reaction with respect to a reactant show?

A

The number of molecules of that reactant that is involved in the rate-determining step . So if a reaction’s second order with respect to X, there’ll be two molecules of X in rate-determining step.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is DYNAMIC EQUILIBRIUM

A

When the forward and background reactions of a reversible reaction are happening at exactly the same rate, so the concentration of reactants and products doesn’t change.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the equation for the equilibrium constant (Kc) ? aA+bB=cC+eE

A

Kc= [D]^d[E]^e/[A]^a[B]^b a,b,c and are the number of moles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How is the position of the equilibrium altered?

A

By changing the conc, pressure or temperature of a reversible reaction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens if the position of the equilibrium shifts to the left?

A

More reactants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What happens if the position of the equilibrium shifts to the right?

A

More products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Le Chatelier’s Principle

A

If there is a change in concentration, pressure or temperature, the equilibrium will shift to counteract the change.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What happens to the equilibrium if you: a) increase the temperature b) decrease the temperature

A

a) adds heat so equilibrium shifts in endothermic direction (+ve ΔH) to absorb heat. b) removes heat energy, equilibrium shifts in exothermic direction (-ve ΔH) to try and replace heat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What will happen to Kc if a temperature change means more product formed?

A

Kc will rise.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What will happen to Kc if a temperature change means less product formed?

A

Kc will decrease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What happens if the conc of one thing in an equilibrium changes and why?

A

The conc. of the others must change to keep the value of Kc the same.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the effect of catalyst n the equilibrium and why?

A

NO effect because a catalyst will increase the rate of both forward an backwards reactions. Equilibrium position will be the same as uncatalysed reaction but equilibrium will be reached faster.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are BRONSTED LOWRY ACIDS?

A

proton donors- they release H+ ions when they’re mixed with water. HA(aq) = H+(aq) +A-(aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What are BRONSTED LOWRY BASES?

A

They’re proton acceptors, when in solution they grab H+ ions from water molecules. B(aq)+H2O(l) = BH+(aq) + OH-(aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Where is the equilibrium for weak/strong acids? HA(aq)=H+(aq) +A-(aq)

A

WEAK- far to left STRONG- far to right

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What to acids and bases do in water?

A

DISSOCIATE- break up into +ve and -ve ions. The amount of dissociation depends on how strong or weak the acid or base is.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

How much do strong acids/ bases dissociate (ionise) in water?

A

Almost completely

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Give one example of a strong acid and a strong base

A

HCl(g)=H+(aq) + Cl-(aq) NaOH(s)=Na+(aq) + OH-(aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

How do weak acids/ bases dissociate in water?

A

Dissociate slightly in water.

36
Q

What needs to be present for acids to release H+ ions?

A

Base to accept them.

37
Q

Give a generic equation for an acid donating H+ ions to a base.

A

HA(aq) + B(aq) = BH+(aq) + A-(aq)

38
Q

Generic equation for a weak acid being added to water.

A

HA(aq) + H2O(l) = H3O(aq) +A-(aq)

39
Q

What is the equation for dissociation of water?

A

H2O(l) + H2O(l) = H3O+(aq) + OH-(aq) Simplifies to: H2O(l) = H+(aq) + OH-(aq)

40
Q

What is the equation for the ionic constant of water (Kw) and how is it formed?

A

Kw=[H+][OH-] Water only dissociates a tiny amount, so equilibrium far to the left. So much water compared to H+ and OH- tha tconc. of water is considered to have a constant value. So multiply Kc equation by H2O: Kc=[H+][OH-]/[H2O] X H2O

41
Q

At 298K (25C) what is the value of Kw?

A

1.00X10-14 mol2dm-6

42
Q

What is the Kw expression for pure water?

A

Kw=[H+]^2 because always one H+ for every OH- so [H+]=[OH-]

43
Q

What is the pH scale a measure of?

A

The hydrogen ion concentration in a solution.`

44
Q

Why is H+ concentration (for pH) measured on a logarithmic scale?

A

Conc. of H+ ions can vary massively.

45
Q

What is the equation for pH?

A

-log[H+]

46
Q

How do you calculate the H+ ion conc. from pH?

A

10^-pH

47
Q

MONOPROTIC ACID

A

Each molecule of an acid will release one proton when it dissociates. e.g. HCl and HNO3

48
Q

How do you figure out pH of monoprotic acids?

A

H+ ion conc. is same as acid conc. Each mole of acid produces one mole of H+ ions.

49
Q

DIPROTIC ACID

A

Each molecule of acid will release two protons when it dissociates. e.g. H2SO4= 2H+ + SO4^2-

50
Q

How do you figure out pH of diprotic acid?

A

Produce two moles of H+ ions for each molecule of acid meaning H+ ion conc. is twice the conc. of the acid. (Times conc. of acid by two for H+ conc. or divide by 2for acid conc.)

51
Q

How do strong bases ionise in water?

A

Fully- one mole of OH- per mole of base. The conc. of OH- ions is the same as conc. of base

52
Q

If you know [OH-] for a strong base and Kw how do you work out the pH?

A

1: Find values of Kw and [OH-]. 2: Rearrange Kw equation, substitute in values and solve to find [H+] 3: Once you know [H+], substitute into pH equation and solve.

53
Q

What is the acid dissociation constant, why do you have to use it and how is the equation derived?

A

Weak acids don’t fully ionise in solution, so [H+] isn’t the same as the acid conc. Have to use acid dissociation constant- Ka. HA=H+ +A- Only a tiny amount of HA dissociates so you can assume [HA] at the start of reaction is the same as [HA] at equilibrium. Ka= [H+][A-]/[HA] When dealing with weak acids you can assume that all the H+ ions come from the acid, so [H+]=[A-]. Simplified to: Ka= [H+]^2/[HA]

54
Q

How do you find the pH of weak acids?

A

1: Write an expression for Ka for weal acid. 2:Rearrange and substitute in values to find [H+]^2. 3:Square root number to find [H+]. 4: Substitute [H+] into pH equation.

55
Q

Finding concentration of weak acids

A

If you already know pH you can use Ka. 1:Sub. pH into inverse pH equation to calculate [H+] . 2: Write an expression for Ka. 3: Rearrange the equation to give conc. of acid. 4: Substitute values for Ka and [H+] into the equation and solve.

56
Q

Why is pKa often used?

A

Value of Ka varies massively from one acid to another .

57
Q

What is the equation for pKa?

A

pKa=-log(Ka)

58
Q

What is the equation for inverse Ka?

A

Ka= 10^-pKa

59
Q

What is the END POINT?

A

The point at which all of the acid is neutralised.

60
Q

How are pH curves plotted?

A

Plot pH of titration mixture against the amount of base added as the titration goes on.

61
Q

Describe the pH curve of a strong base added to a strong acid.

A

The pH starts around 1, as there’s and excess of strong acid. Finishes around pH 13, when excess of strong base.

62
Q

Describe the curce of a weak base being added to a strong acid

A

The pH starts around 1, as there is an excess of strong acid. It finishes around pH9 as there is an excess of weak base.

63
Q

Describe the pH curve of a strong base being added to a weak acid.

A

pH starts around 5, as there’s an excess of weak acid. It finishes around pH 13, when you have an excess of strong base.

64
Q

Describe the pH curve of a weak base being added to a weak acid.

A

pH starts around 5, as there’s an excess of weak acid. It finishes up around pH 9, when excess of weak base.

65
Q

What is the mid-point of the vertical section on a pH curve?

A

The equivalence point/end point . At this point, a tiny amount of base causes a sudden, big change in pH- here that all the acid is neutralised.

66
Q

What is important for an indictor to do?

A

Change colour at exactly the end point of titration.

67
Q

What kind of indicator do you need to use in a titration?

A

One that change colour over a narrow pH range that lies entirely on the vertical part of the pH curve.

68
Q

What are two common indicators used in acid-base titrations?

A

Methyl orange- red at low pH, yellow at high, approx. pH of colour change 3.1-4.4

Phenolphthalein- colourless at low pH, pink at high pH, Approx. pH of colour change 8.3-10.

69
Q

How can you make a titration as accurate as possible?

A
  • Measure the neutralisation volume as precicely as possible, usually to nearest 0.05cm3.
  • Repeat titration at least three times and take a mean average titre value. Make sure result is reliable.
    • Don’t use anomalous results- should all be within 0.2cm3 of each other.
70
Q

How do you calculate concentrations for monoprotic acids?

A

1: Write out balanced equation
2: For one reagent you will know both the concentration and the volume. Calculate number of moles for this reagent using n=cXv(dm3)
3: Use molar ratios in the balanced equation to find out how many moles of other reagent reacted.
4: Calculate unknown concentration using c=n/v(dm3)

71
Q

How do you work out concentration for diprotic acids?

A

Same as monoprotic except twice as many molsof base as acid.

72
Q

What is a buffer?

A

A buffer is a solution that resists changes in pH when small amounts of acid or alkali are added.

A buffer doesn’t stop the pH from changing completely - makes changes very slight though.

Buffers only work for very small amount of acid or alkali.

73
Q

What are acidic buffers? How are they made?

A

Buffers tha thave a pH of less than 7.

They are mad eby mixing a weak acid wuth one of its salts.

74
Q

When do acidic buffers resist changes in pH?

A

When either an acid or a base is added to a solution.

75
Q

A mixtur eof ethanoic acid and sodium ethanoate is an acidic buffer. What allows it to work as a buffer?

A

The ethanoic acid is a weak acid so only slightly dissocites

CH3COOH(aq) <=> H+(aq) + CH3OO-(aq)

BUt the salt fully dissociates when dissolved:

CH3COONa(s) = CH3COO-(aq) + Na+ (aq)

So lots of undissociated ethanoic acid and lots of ethanoate ions.

When you alter the concentration of H+ or OH- in the buffer aolution the equilibrium moves to counteract the change.

76
Q

How does ethanoic acid/sodium ethanoate buffer resist an acid?

A

Large number of CH3OO- ions make sure that the buffer can cope with the addition of acid. If you add a small amount of acid the H+ conc. increases. mOst of the extra H+ combin with CH3OO- ions to form CH3COOH. This shofts equilibrium to the left, reducing H+ conc. to close to its original value. So pH doesn’t change much.

77
Q

How does ethanoic acid/sodium ethanoate buffer resist a base?

A

If a small amount of base (e.g. NaOH) is added, the OH- conc. increases. MOst of the extra OH- ion react with H+ ions to form water- removing H+ ions from the solution. This causes more CH3COOH to dissocate to form H+ ions- shifting equilibrium to the right.

78
Q

What are basic buffers?

A

Have a pH more than 7 made by mixing a weak base with one of its salts.

79
Q

A solution of ammonia (NH3, a weak base) and ammonium chloride (NH4Cl, a salt of ammonia) acts as a basic buffer, what allows it to work as a buffer?

A

The salt fully dissociates in solution :

NH4Cl(aq) = NH4+(aq) + Cl-(aq)

Some of NH3 molecules will also react with water molecules:

NH3(aq) + H2O(l) <=> NH4+ + OH- (aq)

So the solution will contain lots of ammonium ions (NH4+) and lots of ammonia molecules.

80
Q

How does NH3/NH4Cl solution resist an acid?

A

If a small amount of acid is added, the H+ conc. increases, making the solution more acidic. Some of the H+ ions react with OH- ions to make H2O. When this happens the equilibrium shifts to the right to replace OH- ions that have been used up. This reaction will remove most of the extra H+ ions added.

81
Q

How does NH3/NH4Cl resist a base?

A

If a small amount of base is added, the OH- conc. increases, making the solution more alkaline. Most of the extra OH- ions will react with the NH4+ ions, to form NH3 and H2O. So the equilibrium will shift to the left, removing OH- ions from the solution.

82
Q

Where are buffers often used?

A

In shampoo- most contain a pH 5.5 buffer- counteracts alkaline soap in shampoo.

Biological washing powder- buffer keeps pH at right level for enzymes to work best .

Blood- needs to be kept as close to 7.4 as possibl, so contain a buffer system.

83
Q

How do you calculate the pH of a buffer using known concentrations?

A

If you know Ka of the weak acid and conc of the weak acid and its salt.

1: Write out Ka expression of weak acid (e.g. HCOOH)

Ka= [H+][HCOO-]/[HCOOH]

2: Rearrange equation to give expressionfor [H+]
3: Substitute values for Ka, and the concentration of the acid and salt into equation.
4: Solve
5: Substitute [H+] into pH equation

84
Q

What is another way to make an acidic buffer?

A

You could take a weak acid and add a small amount of alkali, so that some of the mixture is neutralised to make a salt, but some is left uneutralised. Reaction mixture woul dthen contain a weak acid and its salt, so would act as an acidic buffer.

85
Q

How do you calculate the pH of the alteranative way of making an acidic buffer?

A

1: Write out quation for neutralisation reaction

acid + base = salt + water

2: Calculate number of moles of acid and base at the start of the reaction using the volumes and concentrations given.
3: Use the molar ratios in the equation to work out the moles of acid and salt left at end.
4: Calculate conc. of the acid and salt in the buffer solution by dividing by the volume of the solution- this is the volume of the acid and base added togther.
5: Calculate pH

Chemistry A2 UNIT 4 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions