Unit 2 - Physical Chemistry Flashcards by Jenny Hartmann

What is chemical equilibrium

When concentration of reactants and products remains constant over time

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Equilibirum must take place in a 1 system

Closed

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What is a closed system

Species in solution can not escape to environment

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What is a stable equilibrium

Usually minimum E state

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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

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K > 1 = (1)

K < 1 = (2)

1 product favoured

2 reactant favoured

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What happens to Kc when heat is added to an expthermic reaction

Decrease

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What happens to Kc if heat is added to an endothermic reaction

Increase

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What reavtion is favoured when heat is added to an exothermic reaction

Reverse reaction

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What reaction eill be favoured if heat is added to an endothermic reaction

Forward reaction

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Acids= H+ donors/acceptors

Donors

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Bases= H+ donor/acceptor

Acceptor

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For every acid there is a (1)

Conjugated base

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For every base there is a (2)

Conjugated acid

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H2O is amphoteric which means..

It can accept and donate protons

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Why is water a poor conductor of electricity

Because it doesnt dissociate very much

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What is Kw

Ionic product of water

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What is Ke dependent on

Temperature

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In pure water, H+ and OH- are

Equal

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Do strong bases and acids dissociate completely or partially

Completely

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Examples of strong acids

HCL, HBr, Hl, HNO3, H2SO4

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What does ph depend on for strong acids

Initial molarity of the acid

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What are common strong bases

Oxides, hydroxides of group 1 metals

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What does [OH-], [H+] and pH depend on for strong bases

Initial molarity of base

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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