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Biochemistry > Chemical reactions > Flashcards

Chemical reactions Flashcards

Bond breaking/making, nucleophiles and electrophiles, mechanisms, chemical energy, thermodynamics, equilibrium, kinetics.

1
Q

Why are some chemical reactions considered to be irreversible?
For example, burning fuels.

A

The products cannot be easily changed back into reactants.

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2
Q

Many chemical reactions are reversible especially in biochemistry, organic chemistry and isomerism.

What do chemical reactions involve?

A

The breaking and making of bonds.

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3
Q

Reactions of organic compounds often involve the breaking and making of covalent bonds, therefore the movement of…

A

electrons.

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4
Q

What shows the movement of a pair of electrons?

A

a double-headed curly arrow

(used to draw chemical mechanisms - a series of steps to show the pathway of a chemical reaction)

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5
Q

How many ways can bond breaking occur? What does it depend on?

A

2 - how many electrons are transferred.

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6
Q

What bond breaking way do we focus on in BIO1332?

A

Heterolytic fission.

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7
Q

What is heterolytic fission?

A

A type of bond-breaking in chemistry where a covalent bond splits in such a way that both electrons from the bond go to one of the two atoms involved, rather than being split equally.

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8
Q

Where do the arrows start and end for heterolytic bond formation?

(If confused, look at summary sheet)

A

Curly arrows must start where the electrons are and end where the bond is formed.

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9
Q

What are nucleophiles?

A

Electron rich ions/molecules with a lone pair of electrons they can use to form a new dative covalent bond.

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10
Q

List 3 anions that are nucleophiles.

A

Cl-, OH -, CN-

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11
Q

List 4 neutral molecules that are nucleophiles.

(If confused, look at RECAP for PowerPoint).

A

H2O, NH3, serine (lone pair on OH group), histidine (lone pair on N).

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12
Q

Nucleophiles react with…

A

electrophiles.

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13
Q

What are electrophiles?

A

Electron deficient ions/molecules which can accept a lone pair of electrons to form a new covalent bond.

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14
Q

List 2 cations that are electrophiles.

A

Carbocations, H+.

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15
Q

List 4 neutral molecules that are electrophiles. Their bonds are…

(If confused, look at RECAP for PowerPoint).

A

polarised.

H-Cl, H3C-Cl, C=O bond in propanal, histidine (slightly positive H attached to N).

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16
Q

What is the OH radical?

A

One of the most reactive biological species.

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17
Q

Which direction do curly arrows always flow in?

A

The direction of electron travel (from the nucleophile to the electrophile).

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18
Q

There are three main acid-base theories, which one do we look at in BIO1332?

A

Bronsted-Lowry theory.

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19
Q

What is an acid?

A

A proton donor (lower pKa values).

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20
Q

What is pH?

A

A measure of the concentration of hydrogen ions.

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21
Q

What is a base?

A

A proton acceptor (higher pKa values).

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22
Q

Lysine and arginine are weaker bases than…

A

histidine.

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23
Q

Acid-base enzyme catalysed reactions utilise amino acid side chains to facilitate…

A

proton transfer.

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24
Q

What is oxidation?

A

A reactant loses an electron (or sometimes gains oxygen).

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25
Q

What is reduction?

A

A reactant gains an electron (or sometimes loses oxygen/gains hydrogen.

26
Q

What are oxidoreductases?

A

Enzymes that catalyse electron transfer during redox reactions.

27
Q

What does the question ‘how much product will form’ relate to?

A

Thermodynamic factors (relating heat, work, temperature and energy).

28
Q

What is the question ‘ how much product will form’ determined by?

A

The equilibrium constant (K).

29
Q

What does the question ‘how fast will the product form’ relate to?

A

Kinetic factors (factors affecting reaction rate).

30
Q

What is the question ‘how fast will product form’ determined by?

A

The rate constant (k).

31
Q

What is chemical energy?

A

The potential energy stored in chemical bonds.

32
Q

What is thermodynamics?

A

The study of the laws that govern the conversion of energy from one form to another.

33
Q

Energy changes are a characteristic feature of chemical reactions.

Many chemical reactions release energy. Give examples.

Some chemical reactions absorb energy.
What is energy measured in?

A

Heat/light/sound/chemical.

Joules (J).

34
Q

What kind of process is bond breaking?
Why?

A

Endothermic - it requires an input of energy (e.g. heat/kinetic).

35
Q

What kind of process is bond making?
Why?

A

Exothermic - energy is released (e.g. light/heat/sound).

36
Q

Reaction profiles follow a reaction’s thermodynamics and…

(look at the summary sheet for a diagram)

A

kinetics.

37
Q

What is Gibb’s free energy change in simple terms?

A

Difference in chemical energy between reactants and products.

38
Q

What does a negative Gibb’s free energy change mean for a reaction?

A

It’s thermodynamically favourable and spontaneous (once started, the reaction occurs by itself without any external energy).

39
Q

What does a positive Gibb’s free energy change mean for a reaction?

A

It’s thermodynamically unfavourable and non-spontaneous (reaction requires application of constant external energy.

40
Q

HCl + (CH3)3 ⇌ (CH3)3CCl + H2O
What is present at the ‘end’ of the reaction?

A

Both starting materials and products.

41
Q

Define equilibrium.

A

The rate of the forward reaction is equal to the rate of the reverse reaction.

The concentrations of the reactants and products do not change.

42
Q

How is the equilibrium constant K calculated?

A

[products]/[reactants]

43
Q

What do values for K>1 imply?

A

A high concentration of products at equilibrium.

44
Q

What do values for K<1 imply?

A

A low concentration of products at equilibrium.

45
Q

For the particular reaction looked at, as the temperature increases, K increases.
What does this imply?

A

More product is will be made at higher temperatures.

46
Q

How does Gibbs free energy link to the equilibrium constant?

A

∆G = -RTlnK

47
Q

If ∆G is negative K is…

A

> 1.

48
Q

What is kinetics?

A

The study of rates of reaction.

48
Q

If ∆G is positive K is…

A

< 1.

49
Q

Reactions with large equilibrium constants do not always occur rapidly.
What needs to happen for a reaction to occur between two molecules?

A
  • The molecules must collide with each
    other.
  • Molecules must collide in an orientation
    that facilitates bond making/breaking.
  • Have activation energy (sufficient energy
    to start the reaction.
50
Q

The activation energy determines how fast a reaction will go that is…

A

thermodynamically favourable.

51
Q

Slower reactions have higher activation energies than…

A

faster ones.

52
Q

What is the rate constant, k?

A

A measure of the speed of a chemical reaction (independent of concentration).

53
Q

A higher rate constant means a…

A

faster reaction.

54
Q

Write the Arrhenius equation.

A

k = Ae^(-Ea/RT)

55
Q

A lower activation energy means a larger value for k so a…

A

faster reaction.

56
Q

A higher temperature means a larger value for k so a…

A

faster reaction.

57
Q

What are catalysts?

A

Compounds that speed up a chemical reaction without undergoing any permanent chemical change.

58
Q

What are enzymes known as?

A

Biological catalysts.

59
Q

How do catalysts increase the rate of chemical reactions?

A

Provide an alternative reaction pathway with a lower activation energy.

Biochemistry (10 decks)

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