chem final

• Chromium (III)


  Cr (3+ charge)

  - green colour
• Cobalt (II)


  Co (2+ charge)

  - pink colour
• Copper (I)


  Cu+

  - green colour
• Copper (II)


  Cu (2+ charge)

  - blue (sometimes green?)
• Permanganate


  MnO4 -

  - purple
• Chromate


  CrO4 (2- charge)

  - yellow
• Dichromate


  Cr2O7 (2- charge)

  - orange
• Iron (II)


  Fe (2+ charge)

  - pale green
• Iron (III)


  Fe (3+ charge)

  - yellow/brown
• manganese


  Mn (2+ charge)

  - pale pink
• nickel (II)


  Ni (2+ charge)

  - green
• Irreversible Reactions


  - Chemical reactions that proceed in one direction only

  - the reactants keep changing to the products until at least one of the reactants is used up

  - These reactions will go to completion
• Examples of irreversible reactions

  - reactions of metals with dilute hydrochloric acid

  - Acid-alkali neutralization
• Reversible Reactions


  - Do not go to completion

  - the products of these reactions can react to give the starting reactants
• forward reaction


  when the reaction proceeds from the left to the right

  A + B <=> C + D

  - products are C and D

  - Reactants are A and B
• backward reaction


  when the reaction proceeds from the right to the left

  C + D <=> A + B

  - Products are A and B

  - Reactants are C and D
• Examples of reversible reactions

  - Esterfication

  - Ionization of ethanoic acid
• Esterfication


  - upon heating ethanoic acid reacts with ethanol

  - Ethyl Ethanoate and water are produced

  - reaction does not go to completion

  - ethyl ethanoate reacts with water to give ethanoic acid and ethanol

  - this shows the reaction proceeds in both directions
• Heating under reflux

  - why use with ethanol

  Heating a reaction mixture with a condenser fitted vertically

  - ethanol is volatile and heating under reflux prevents the loss of ethanol before it reacts
• Ionization of ethanoic acid

  - weak acids ionize only partially in water

  - ethanoic acid ionizes only slightly in water to form ethanoate ions and proton

  - ethanoate ions and hydrogen ions combine to form ethanoic acid molecules

  - resultant solution contains mainly ethanoic acid molecules and a very small proportion of ethanoate ions and hydrogen ions
• Equilibrium of a reversible reaction

  - when the rates of forward and backward reactions become equal

  - there is no observable change in the chemical system

  - the forward and backward reactions are still continuing, it is dynamic in nature

  - can be established in a physical system and a chemical system
• Physical Equilibria


  - requires a closed system at constant temperature

  - examples are dissolving and evaporation
• What happens when equilibrium is reached

  - the decomposition of reactants is the same as the rate of combination of the products

  - the forward and backward rates are equal

  - the colour intensity and concentrations of the mixture remain unchanged
• Dynamic equilibrium can be reached

  from either direction of a reversible reaction
• Why is a closed system important for the establishment of a dynamic equilibrium

  - If any of the reaction mixture escapes it will never establish an equilibrium
• At dynamic equilibrium, both ____ and ____ are...

  products and reactants are present and their concentrations remain unchanged. Hence, there are no observable changes of the reaction mixture
• At dynamic equilibrium, the rate of forward reaction is ...


  equal to the rate of backward reaction
• Dynamic equilibrium can be reached from either the ...

  forward or backward direction of the reversible reaction
• Dynamic equilibrium can only be established in a ...

  closed system, where no materials can enter or exit the system
• what is Kc


  equilibrium constant

  - a ratio with a constant value for a reaction at equilibrium at a given temperature

  - the subscript c indicates that it is expressed in concentration
• equilibrium law


  - the mathematical relationship between the equilibrium concentrations of reactants and products

  - shown as products over reactants = Kc in equation
• Homogeneous equilibrium


  an equilibrium system in which all the reactants and products are in the same state

  - represented using normal rate law equation

  - if (l) and (aq) are in an equation together it counts as homogeneous
• Heterogeneous equilibrium


  an equilibrium system in which two or more phases are present

  - represented using only gaseous and inaqueous substances
• Why can solids and liquids be simplified out of rate law equations

  - the concentration of pure solids and liquids in heterogeneous equilibria do not appear in the expression of Kc

  - pure liquids and solids are 'constants' and can be simplified
• What does the magnitude of Kc tell us

  - the composition of the reaction mixture

  - provides useful indication of the extent of a chemical reaction (how far a reaction proceeds to completion)

  - indicates the extent of a chemical reaction at equilibrium but not the rate of the reaction
• What does a large Kc tell us

  - tells us that most of the reactants are converted into products at equilibrium

  - The reaction proceeds almost to completion
• What does a small Kc tell us

  - tells us that only very small amounts of products form at equilibrium

  - the reaction hardly happens at all
• what does Le Chatelier's Principle state

  states that when a chemical system at equilibrium is disturbed by a change in conditions, the equilibrium position will shift in a direction that tends to counteract the change
• If Kc is large (much greater than 1) how does it affect the equilibrium position

  - the equilibrium position will lie to the product side

  - the products dominate the reaction mixture at equilibrium
• If Kc is small (much smaller than 1) how does it affect the equilibrium position

  - the equilibrium position will lie to the reactant side

  - the reactants dominate the reaction mixture at equilibrium