Unit 2 - Physical Chemistry Flashcards
What is chemical equilibrium
When concentration of reactants and products remains constant over time
Equilibirum must take place in a 1 system
Closed
What is a closed system
Species in solution can not escape to environment
What is a stable equilibrium
Usually minimum E state
Whats a dynamic equilibrium
Where concentration of reactants and products remain the same but the individual molecules/ ions are moving from one side of the euqation to the other side
Forward and reverse are equal
K > 1 = (1)
K < 1 = (2)
1 product favoured
2 reactant favoured
What happens to Kc when heat is added to an expthermic reaction
Decrease
What happens to Kc if heat is added to an endothermic reaction
Increase
What reavtion is favoured when heat is added to an exothermic reaction
Reverse reaction
What reaction eill be favoured if heat is added to an endothermic reaction
Forward reaction
Acids= H+ donors/acceptors
Donors
Bases= H+ donor/acceptor
Acceptor
For every acid there is a (1)
Conjugated base
For every base there is a (2)
Conjugated acid
H2O is amphoteric which means..
It can accept and donate protons
Why is water a poor conductor of electricity
Because it doesnt dissociate very much
What is Kw
Ionic product of water
What is Ke dependent on
Temperature
In pure water, H+ and OH- are
Equal
Do strong bases and acids dissociate completely or partially
Completely
Examples of strong acids
HCL, HBr, Hl, HNO3, H2SO4
What does ph depend on for strong acids
Initial molarity of the acid
What are common strong bases
Oxides, hydroxides of group 1 metals
What does [OH-], [H+] and pH depend on for strong bases
Initial molarity of base
Is Ka large/small for strong acids
Large
Why is Ka large for strong acids
Because they dissociate completely
Pka for strong acids is
Small
Pka for wear acids is
Large
Pka for weak conjugated base is
Small
Pka for strong conjugated base is
Large
Strong acids and bases dissociate (1) in awueous solutions
Completely
Weak acids and bases dissociate (2) in aqueous solutions
Partially
What does ph in a salt solution depend on
Relative strength of parent acid and base
Strong acid + strong base =
Neutral
Weak acid + strong base =
Alkaline
Strong acid + weak base =
Acidic solution
Whats a buffer solution
A solution in which the ph remains approximately constant when small amounts of water (acid) base are added
Whats an acid buffer
Solution if weak acid + on eof its salts
Whats a basic buffer
Solution of weak base + one of its salts
What must a buffer be able to do in order to stabalise ph
Absorb extra acid or alkali
How does an acid buffer work
Weak acid provides H+ and when these are removed by the addition of small amounts of base.
The salt of the weak acid provides the conjugated base which can absorb exess H+ produced bt addition of a small amount if acid
What are indicators
Dyes ehose colours are sensitive to pH
What can indicators be used for
Determine the end point of an acid - base titration
What is thermochemistry
The study of chages in E that occur in chemical reactions
What does reaction feasibility depend on
Enthalpy
Temp
Entropy
What is the standard enthalpy of formation
Enthalpy change when one mole of substance us formed from its elements un their standard states
Whats the standard state of a substance
Its most stable state at a pressure of 1 atm and a specific T
Whats the standard enthalpy
Can be calculated form the standard enthalpies of formation of the reactants and products
Whats entropy
Degree of disorder of a system
Increased disorder= 1 entropy
Increased
Solids have high/low disorder
Low
Gases have high/low disorder
High
Why do gases have a higher entropy than solids
Because gases can move more freely while solid particles are limited to vibration
What do state changes do to entropy
Large changes in entropy
Whats the 2nd law of thermodynamics
The total entropy of a reaction system and its surroundings always increases for a spontanious process
Heat energy released into surroundings
Increased S of surroundings
Heat energy absorbed from surroundings
Decreased S of surroundings
Whats the standard entropy of a substance
Entropy value for the substance in uts standard state
Whats a feasible reaction
One that tends towards the product rather than the reactants
What needs to happen for a reaction to be feasible at given T
Must happen spontaneously
What happens when a reaction occurs spontaneously
No extra energy needed for reaction to occur
What do kinetics describe
The rate of chemical reactions
What is the rate determining step
Step which is the slowesr and therefore contributes the most to the rate
