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Chemistry Of Biological Interactions: > Biomolecular Reactions: > Flashcards

Biomolecular Reactions: Flashcards

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1
Q

What is an endothermic reaction?

A

A reaction in which the products have a greater chemical potential energy than the reactants

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2
Q

What is required to start an endothermic reaction?

A

The input of energy in the form of heat

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3
Q

What is an exothermic reaction?

A

A reaction where the reactants have a chemical potential energy than the products

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4
Q

What is required to start an exothermic reaction?

A

Energy must be given out in the form of heat

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5
Q

What is the equation for Gibbs energy ? State what each symbol means:

A

G = H-TS

  • H is enthalpy
  • T is temperature
  • S is entropy
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6
Q

What is the change in Gibbs energy equal to?

A

The enthalpy change of the system minus the product of the temperature and the change in the entropy of the system
△G = △H - T△S

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7
Q

What is a catalyst?

A

A substance that increases the reaction rate without being consumed

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8
Q

How do catalysts work?

A
  • Catalysts provide an alternative reaction pathway with a lower activation energy
  • Provides an alternative reaction mechanism in which the transition state is more stabilised
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9
Q

What is a nucleophile?

A

An electron-pair donor that participates in bond formation by donation of an electron pair to an electron acceptor

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10
Q

What is an electron acceptor?

A

An electrophile

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11
Q

What is an electrophile?

A

An electron-pair acceptor that participates in bond formation by accepting an electron pair from an electron donor

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12
Q

What is an electron donor?

A

A nucleophile

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13
Q

What is a system?

A

The system is simply the set of biochemical reactions and interactions we are interested in studying within a particular boundary

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14
Q

What are examples of a system?

A

The reactants and products in a reaction

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15
Q

What are surroundings?

A

Everything else that is outside the system of interest that is in contact with the boundary of the system (usually the rest of the universe).

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16
Q

What is a boundary?

A

Where the system and surroundings meet

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17
Q

What are the three main ways a system and its surroundings are described?

A
  • Open
  • Closed
  • Isolated
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18
Q

Describe the energy transfer in an open system and its surroundings:

A

Energy and mass is transferred both ways between a system and it’s surroundings

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19
Q

Describe transfer between a closed system and it’s surroundings:

A

A transfer of energy (only) between the system and the surroundings

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20
Q

Describe the energy transfer between an isolated system and it’s surroundings:

A

There is no transfer of energy or mass between the system and surroundings

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21
Q

What effect does the boundary between the system and it’s surroundings have?

A

The boundary plays no part (does not affect or is affected by) interactions between, or behaviours of, the system and the surroundings

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22
Q

What is the law of conservation of energy?

A

Energy can neither be created nor destroyed but changed from one form to another

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23
Q

What is the law of conservation of energy the basis of?

A

The First Law of Thermodynamics

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24
Q

What does it mean that energy can only be transferred from one form to another, and not created or destroyed?

A
  • The total energy of an isolated system doesn’t change

- The total energy of a system and its surroundings does not change

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25
Q

Describe energy transfer when an object is dropped from a height:

A

Stored (potential) energy in the form of gravitational potential energy is transformed into kinetic energy

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26
Q

Why is energy transformed from potential energy to kinetic energy when an object is dropped?

A

The gravitational potential energy does work, upon release, to give the object kinetic energy as it falls

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27
Q

What are the two types of stored (potential) energy?

A
  • Gravitational potential energy

- Chemical energy

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28
Q

What is chemical (potential) energy?

A

A type of potential energy related to chemical bonds

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29
Q

What is thermodynamic temperature?

A

An absolute measure of the average total internal energy of an object or objects (mainly the kinetic energy and other other contributing factors)

30
Q

What is the normal measure of temperature?

A

A direct comparison of how cold/hot something is relative to another

31
Q

What is thermodynamic temperature defined by?

A

The third law of thermodynamics

32
Q

What in the third law of thermodynamics defines the thermodynamic temperature?

A

The theoretically lowest temperature is 0 K which is equivalent to -273.15 °C

33
Q

What is thermodynamic temperature measured in?

A

Kelvin (K)

34
Q

What is thermodynamic temperature proportional to?

A

The average of all energies in all the ways in which it is possible for an object to move

35
Q

what is the name given to the average of all the energies in all the ways in which it is possible for an object to move?

A

Degrees of Freedom

36
Q

Explain why a helium atom only has 3 degrees of freedom:

A

It can move in the up and down plane, left and right plane and the front and back plane

37
Q

How many degrees of freedom does a two atom molecule (like nitrogen) have?

A

Five degrees of freedom

38
Q

Why do two-atom molecules have five degrees of freedom?

A

They can move:
- Front and back

  • Left and right
  • Up and down
  • Rotate
  • Vibrate
39
Q

What effect does the size of a molecule have on the degrees of freedom?

A

The more components (increasing the complexity of the molecule), the greater the number of possible motions (degrees of freedom).

40
Q

What happens when two objects with different temperatures come into contact?

A

They will eventually reach the same temperature

41
Q

Why do two touching objects eventually end up having the same temperature?

A

Heat is transferred from one object to other in order to reach this thermal equilibrium

42
Q

What is enthalpy? Define both terms:

A
  • The internal energy of a system plus the amount of pressure and volume
  • The total amount of energy (the sum of the heat/kinetic and chemical potential energy) that a chemical system possesses
43
Q

What is the enthalpy change in a system equal to?

A

The heat brought in or released to the system at constant pressure

44
Q

What can kinetic energy be in the form of?

A
  • Moving electrons within an atom
  • The vibrations of atoms connected by chemical bonds
  • The rotation and translation of molecules made up of these atoms
45
Q

What can chemical potential energy be in the form of?

A
  • Covalent or ionic bonds between atoms/ions

- Intermolecular forces between molecules

46
Q

What is the symbol for enthalpy?

A

H

47
Q

How do we work out the enthalpy change of a reaction?

A
  • Add up the bond energies for all the bonds in the reactants and products
  • Take away the total bond energy of the products from the bond energy total of the reactants
48
Q

What is bond energy?

A

The average amount of energy required (when substance is a gas and under standard conditions) to break 1 mol of all bonds of the same type within the same chemical species

49
Q

What makes bonds between atoms differ in bond energies?

A
  • Types of atoms involved
  • Types of bonds that exist
  • The surrounding atoms/ the molecule the bond is in
50
Q

What is the average bond energy of a C-H single bond?

A

412 kJ mol^-1

51
Q

Why are bond energies important?

A
  • Tells us how much energy is required to break a particular bond
  • Tells us how much energy will be released when a particular bond is made
52
Q

What can you work out from the total bond energies of the reactants and products?

A

Whether the reaction will take in or release energy when it occurs

53
Q

What is the symbol for enthalpy change?

A

△H

54
Q

What is the equation for calculating the enthalpy change for a chemical reaction?

A

△H = H (products) - H (reactants)

55
Q

What does the symbol △H° mean?

A

The change in enthalpy under standard state conditions

56
Q

What is the standard temperature?

A

298.15 K

57
Q

What is the standard pressure?

A
  • 1 atmosphere (atm)

- 101.325 kPa (SI units)

58
Q

What does △H > 0 show?

A

That a reaction is endothermic

59
Q

Why do endothermic reactions have a positive value for the change in enthalpy?

A
  • Endothermic reactions require energy input in the form of heat.
  • The products have a greater chemical potential energy than the reactants as more energy was taken in for bond breaking in reactants than released for bond making in products
60
Q

What does △H < 0 show?

A

An exothermic reaction

61
Q

Why do exothermic reactions have a negative value for enthalpy change?

A
  • The reactants have a greater chemical potential energy than the products
  • This is as more energy is given out during bond making in the products than bond breaking in the reactants
62
Q

What is more stable, reactants or products, in an exothermic reaction? Why?

A

The products are more stable as their total bond enthalpy is greater

63
Q

What law supports that how or how fast a reaction happens doesn’t influence the overall change in enthalpy for the reaction?

A

Hess’s law

63
Q

What law supports that how or how fast a reaction happens doesn’t influence the overall change in enthalpy for the reaction?

A

Hess’s law

64
Q

What is Hess’s law?

A

The total enthalpy change that occurs for a given reaction is independent of the reaction pathway

65
Q

What diagram is used to show the enthalpy change between reactants and products of exothermic and endothermic reactions?

A

Reaction profiles

66
Q

What does energy spontaneously do?

A

Disperse from being localised to becoming spread out if not hindered from doing so

67
Q

What is entropy?

A

The thermodynamic measure of the randomness of a system

68
Q

What is entropy described as? Why?

A

The thermal energy not able to do work since energy becomes more evenly distributed as the system becomes more dispersed

69
Q

When is entropy important in biomolecular reactions

A

Chemistry Of Biological Interactions: (4 decks)

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