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CH106: Chemistry Principles and Practice 1 > Physical Chemistry > Flashcards

Physical Chemistry Flashcards

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1
Q

What is the Equilibrium Position ?

A

When reactants are mixed together a reaction will proceed towards products until this point is reached.

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2
Q

The equilibrium is dynamic- expand on this…

A

Reactions are still taking place at equilibrium in the forward and reverse reactions but the concentrations of the reactants/products remain constant.

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3
Q

What happens to the rate when a system is not at equilibrium ?

A

The forward and reverse reactions both occur but at different rates and hence there is a change of concentration.

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4
Q

Name an example on an equilibrium reaction involving Nitrogen:

A

Haber Process
N2 + 3H2 <=> 2NH3

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5
Q

Equilibrium favours the products when K is …

A

Greater than 1 (K>1)

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6
Q

Equilibrium favours the reactants when K is …

A

Less than 1 (K<1)

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7
Q

How do you calculate the equilibrium constant ?

A

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

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8
Q

What is used to calculate the equilibrium constant ?

A

Molar concentration

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9
Q

K(back)=

A

1/ K(forward)

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10
Q

How do you calculate the equilibrium constant of the reverse reaction ?

A

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

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11
Q

How do you calculate K(muit) ?

A

K(muit)=( [A]^a[B]^b/ [C]^c[D]^d )^n

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12
Q

When K<1 then…

A

equilibrium lies to the left hence there is no yield

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13
Q

When K >1 then …

A

equilibrium lies to the right hence there is a good yield.

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14
Q

When K~1

A

[Reactants]~[products] - minimal yield

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15
Q

What is Homogeneous ?

A

All reactants and products in a single phase

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16
Q

What is Heterogenous ?

A

Reactants and products exist in different phases.

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17
Q

Why is liquid and solids not included in equilibrium ?

A

They have a fixed concentration

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18
Q

How do you combine equilibria ?

A
  1. Combine reactants
  2. Reverse reaction if need (Kback= 1/Kforw)
  3. Balance (Kmulti = K^n)
  4. Add reactions and cancel species
  5. Find K
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19
Q

What is an Exothermic reaction ?

A

Releases heat energy (-ve ΔH)

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20
Q

What is an Endothermic reaction ?

A

Absorbs heat energy (+ve ΔH)

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21
Q

What affects the equilibrium constant ?

A

Temperature

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22
Q

How does temperature effect K ?

A

Rate almost always increases at higher temperature

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23
Q

How does K relate to rate ? (formula)

A

rate (forward) = K forward [Reactants]
rate (backwards) = K backwards [Products]

24
Q

What is an ice table ?

A

Reactants, Products
Initial concentration
Change in concentration
Equilibrium concentration

25
Q

What are the steps for calculating equilibrium using ICE table ?

A
  1. Balance Equation
  2. ICE table
  3. Find initial data
  4. Find change in stoichiometry
  5. Find equilibrium conc. by solving for X
  6. use equilibrium constant formula
26
Q

How do you calculate Qc ?

A

Qc = [Concentration products]/ [concentration reactants]

27
Q

What does Qc < Kc mean ? (forward or reverse)

A

forward

28
Q

What does Qc = Kc mean ?

A

Reaction is at equilibrium

29
Q

What does Le Chateliers Principle state ?

A

“If a system at chemical equilibrium is disturbed by changing the reaction conditions, the composition of the system will change in order to minimise the effect.”

30
Q

What effect does adding reactant have on the K ?

A

Adding reactant, increases concentration of product

31
Q

What effect does removing product have on K ?

A

Removing product, decreases concentration of reactant

32
Q

What effect does increasing pressure have on a reaction where there are 3 moles of reactant and 2 moles of product ?

A

Increases product yield

33
Q

What effect does adding an Inert gas have on equillibria ?

A

No effect - as the concentration is unaffected

34
Q

What two things in a reaction does temperature effect ?

A
  1. Equilibrium position
  2. The rate at which equilibrium is reached
35
Q

What effect does increasing temperature have on an exothermic reaction ?

A

Decreases yield and reverse reaction is favoured

36
Q

What can reduce the time taken for a reaction to reach equilibrium and what are the exceptions to this ?

A
  • Adding a catalyst
  • Increasing temp - if reaction is exothermic- this must be controlled between speed and yield.
37
Q

What is a catalyst ?

A

A catalyst reduced the activation energy hence speeds up the rate at which equilibrium is reached. A catalyst is involved in the reaction but if not involved in the reaction.

38
Q

What are some examples of HETEROGERNOUS catalysts and how do they work ?

A

Example: Solids such as metals or metal oxides.
The catalyst absorbs onto the surface of the molecule and the reaction takes place at interface.

39
Q

Exothermic is +ve true or false ?

A

False

40
Q

Hess’s law states…

A

“If a chemical reaction can be written as the sum of two other reactions, the heat absorbed at constant pressure will be the sum of values for separate reactions.”

41
Q

What is ‘Enthalpy of formation’ ?

A

Enthalpy for a reaction in which a compound is formed directly from its elements

42
Q

What is the ‘First law of thermodynamics’ ?

A

“The total energy of an isolated system is constant - energy can be transformed by not destroyed.”

43
Q

What does Won stand for ?

A

Work done ON the system

44
Q

What does qIN stand for ?

A

Heat transferred INTO the system

45
Q

What is the delta U ?

A

Internal energy

46
Q

What is the equilibrium constant for water ?

A

K = [H3O][OH-]

47
Q

What is an acid ?

A

Capable of donating protons

48
Q

What is a base ?

A

Capable of accepting protons

49
Q

Amphiprotic meaning

A

Can function as both an acid and a base

50
Q

How do you calculate the equilibrium constant for a WEAK ACID ?

A

K = [H+][A-]/[HA]

51
Q

As Ka increases what happens to strength of acid ?

A

increases

52
Q

As Ka increases what happens to strength of base ?

A

Decreases

53
Q

Some compounds have multiple Ka values, why does this happen ?

A

The negative charge on the anion makes it harder to remove protons

54
Q

What is the Henderson-Hasselbalch equation (H-H) ?

A

pH = pKa + log10 [conj base]/[conj acid]

55
Q

What makes a buffer ?

A

Weak acid and salt of conj base
Weak base and salt of conj acid

CH106: Chemistry Principles and Practice 1 (5 decks)

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