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Chemistry 90% > Equilibrium & energy > Flashcards

Equilibrium & energy Flashcards

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1
Q

ΔG is important for biology

A
  • indicates if a process will or will not occur
  • indicates how far from the equilibrium a process is
  • indicates how much useful work may be available from the process
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2
Q

IfΔG < 0
IfΔG > 0
IfΔG = 0

A

IfΔG < 0 exergonic process
IfΔG > 0 endergonic process
IfΔG = 0 the system is at equilibrium

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3
Q

IfΔG is negative

A

the reaction is spontaneous, energy releasing (exergonic process)

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4
Q

IfΔG is positive

A

the reaction is non- spontaneous, with energy supplied (endergonic process – energy is absorbed)

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5
Q

GIBBS free energy change

A

ΔG =ΔH- TΔS

ΔG = free energy in the system 
ΔH = change in system’s heat content (enthalpy)
ΔS = change in system’s entropy
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6
Q

The first & second thermodynamics are connected by_________

A

GIBBS free energy change

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7
Q

Natural process always move towards __________ disorder

During some process, the entropy in the system______________

A

increasing disorder

decreases, i.e. the system becomes more ordered, accompanied by work being done.

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8
Q

Unit for Entropy

A

ΔS , joules per degree (J/K or JK-1)

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9
Q

Absolute temperature is measured on

A

measured on the kelvin scale

273 K = 0C -273C =0 K

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10
Q

Third law of thermodynamic

A

only in the case of pure, crystalline substance at a temperature of absolute zero would the entropy be zero

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11
Q

Second law of thermodynamic

A

Since energy cannot be created or destroyed, it can only be re-arranged

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12
Q

First law of thermodynamic

A

Conservation states that energy is always conserved, it cannot be created or destroyed

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13
Q

Hee’s Law

A

the enthalpy change in the reaction doesn’t depend on the reaction pathway

ΔHx =ΔH1 +ΔH2

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14
Q

When writing thermochemical equation:

A
  • Numbers of moles
  • State of substance
  • Specify temp the reaction is carried out at
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15
Q

ΔH

A

enthalpy change - the energy change per number of moles

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16
Q

Standard enthalpy of reaction

A

the energy change of a reaction

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17
Q

Standard enthalpy of combustion

A

the enthalpy change when 1 mole of substance is completely burned in excess oxygen under standard situation

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18
Q

Standard enthalpy of formation

A

the enthalpy change when 1 mole of compound is produced from its elements in standard conditions, all products and reactants in the standard state

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19
Q

Bond dissociation enthalpy (bond energy)

A

the energy needed to break one mole of chemical bonds

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20
Q

Change in enthalpy (enthalpy of reaction) formula

A

ΔH = H(products) – H(reactants)

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21
Q

Units for energy

A

joules or kilojoules (kJ)

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22
Q

Enthalpy

A

the energy associate with an element or compounds

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23
Q

System -
Isolated system –
Surrounding -

A

System - the objects been study
Isolated system – the objects which energy is impossible to transform to/ from
Surrounding - everything else in the universe

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24
Q

Thermochemistry

A

the study of the quantity of heat absorbed or evolved by chemical reactions

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25
Q

Thermodynamics

A

the science of the relationship between heat and other form of energy

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26
Q

Factors that affect reaction rate

Explain

A

~Concentration of reactants > effective collisions occur per unit time

~Temperature > speed up the movement of substance, increase chance of collisions

~ Presence of catalyst > A substance that can speed up the reaction, but chemically unchanged at the end of the reaction

~ Surface area > Increase chances of particles contact
~ Pressure (Gaseous reaction) – Increase the amount of particles in the same volume

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27
Q

In kinetic term, Ea is ?

A

the minimum amount of energy which colliding particles need in order to react with each other

28
Q

ΔH

A

The difference between energy level of the reactants and products = the amount of energy taken in or given out during reaction

29
Q

From the top of the curve to the products, going down the energy scale > ?

A

> Energy is given out as bonds are formed in products

Energy put in is less than energy given out > exothermic reaction

30
Q

If the curve is going up the scale, energy is ________

At the top of the curve, bonds in the reactants are ______________

A
  • energy is put in to break bond in the reactants.

- the bonds in the reactants have been broken.

31
Q

ΔG

A

Free energy change

32
Q

Activation Energy (Ea)

A

Minimum amount of energy required for the reaction to start

The amount of energy put in to breaks these bonds

33
Q

Endothermic –

Exothermic –

A

Endothermic – energy taken in for reaction

Exothermic – reaction release energy

34
Q

_______ energy need to break strong bond; _______ energy need to break weak bond

A

More energy need to break strong bond; less energy need to break weak bond

35
Q

Energy is stored in________

A

intramolecular bond (covalent/ ionic/ metallic)

36
Q

Bonds can be __________ during chemical reactions

Energy is _________to break bond

A
  • rearranged

- required

37
Q

Why need energy?

A
  • Mechanical work e.g. muscle contraction
  • Generate light & electricity
  • Active transport, neurotransmitter
  • Synthesis complex biomolecules using simple precursors
38
Q

Kinetic

A

a movement of waves, electrons, atoms, molecules, substances, and objects

39
Q

Potential (Stored)

A

E.g. Chemical energy is the energy stored in the bonds of atoms & molecules

40
Q

What don’t appear in a heterogenous equilibrium constants

A

~ Solid concentration can’t change because it’s molecular weight and density are constant

~ Pure liquid concentration doesn’t vary, they don’t appear in the equilibrium expressions

41
Q

heterogenous equilibrium constants formula

A

Kc = [C][D] / [A][B]2

42
Q

Equilibrium constant formula in a homogenous system

A

Kc = [C]^c[D]^d / [A]^a[B]^b

Kc = equilibrium of concentration
[ ] = concentration in mol/dm3
a = Number of substance
Right hand side of equation on top / left hand at the bottom

43
Q

What gives the equilibrium constant?

A

Measure concentration of everything when a reaction reaches the equilibrium

44
Q

Equilibrium constant allows us to ________

A

to make qualitative judgment about the reaction, if the mixture is mostly products or mostly reactants

45
Q

Le Chatelier’s Principle for changes in pressure

A
  • Changes in Volume of Gaseous Equilibrium Systems
  • Gas volume is related to gas pressure - a gas at reduced volume has a higher pressure (more chance of collisions)
  • A gas at increased volume has a lower pressure
46
Q

How to set up the dynamic equilibrium

A

the rates of the forward reaction and the back reaction have to become equal.
This doesn’t happen instantly. For a very slow reaction, it could take years!
A catalyst speeds up the rate at which a reaction reaches dynamic equilibrium.

47
Q

Le Chatelier’s Principle

A

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change

Eg. changing concentration, pressure (for gaseous reactions) or temperature, or adding more molecules.

48
Q

Heterogenous equilibria

A

Products/reactants in more than one phase

49
Q

Homogenous equilibria

A

everything in the equilibrium mixture is present in the same phase

50
Q

Dynamic equilibrium

A

the forward/ reverse reaction is continuing and the rate of both reactions are equal

51
Q

Chemical equilibrium

A

Reaction can go forward or reversed, occurring at the same rate without net change in energy

52
Q

The tendency for a reaction to reach a equilibrium is driven by

A

the Gibbs free energy (ΔG )

53
Q

K(eq)

A

equilibrium constant

K(eq)= [C][D] / [A][B]

54
Q

Formula of relationship between GIBBS free energy change and equilibrium constant

A

ΔG ^0 = -RT. In.K(eq)

55
Q

Redox reaction

A

transfer of e -
Reduction - gain e-
Oxidation - lose e-

56
Q

Chemical that oxidised is the ______ agent

Chemical that reduced is the _______ agent

A

oxidised, reducing agent

rreduced, oxidising agent

57
Q

redox potential

A

A measure of the tendency for a species to gain or lose electrons

58
Q

Redox potentials are measured in

A

volts (E°)

59
Q

negative value of (E°) tend to ______

Positive value of (E°) tend to ______

A

negative value of (E°) tend to oxidise

Positive value of (E°) tend to reduce

60
Q

Oxidation number

A

losing e- , increasing in oxidation number

gaining e- , decreasing in oxidation number

61
Q

How to calculate the bond energy

A
  1. Balance equation
  2. Draw the structure
  3. Count the bonds and add up bond energy on both side
  4. Calculate ΔH = energy of bond broken - energy of bond formed (kJ/mole)
62
Q

Bond energy (bond dissociation energy)

A

energy required to break bond
a measure of chemical bond strength
Alternative way to find out enthalpy change

63
Q

Breaking bond _______ energy

Forming bond ________ energy

A

Breaking bond need energy

Forming bond release energy

64
Q

Rules of thermochemical equation

A
  1. enthalpy is directly proportional to mass
  2. ΔH for a reaction is equal in magnitude but opposite in sign to ΔH for the reverse reaction
  3. It is independent of the number of chemical steps involved (Hee’s Law)
65
Q

Rules for redox reaction

A
  1. Half the equation
  2. understand the e- transfer directions
  3. Balance the charges
  4. Put 2 side back together

Chemistry 90% (7 decks)

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