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- reactants react together to form the products vice versa
- two processes are equal in their rates, rate forward = rate backwards
- After a certain time the direct reaction and the inverse reaction occur at the same rate = chemical equilibrium
Characteristics of the Equilibrium Condition
- -dynamic has both forward and reverse reactions occurring at the same rate.
- -is no observable change even though reactions are occurring in order to maintain the state of equilibrium.
- -system reacts spontaneously to reduce an imposed stress in order to re-establish a state of equilibrium.
- e.g. physical equil: equilibrium of water vapor with liquid water in a partly filled sealed bottle. only changed from liquid to vapor.
- -chemical equil: Bond breaking and bond formation is involved. An example would be the dissociation of acetic acid .
- temperature must remain constant.
- external pressure must remain constant.
- Once the reaction has begun, no substances are added to the system = isolated and sealed.
Factors That Can Modify Chemical Equilibrium:
concentration of a solute reactant is increased, the equilibrium position shifts to use up the added reactants by producing more products.
Changes in Pressure of Gaseous Equilibrium Systems
- ONLY affects gases
- Increasing the pressure on this equilibrium system will result in the equilibrium position shifting to reduce the pressure, that is, to the side that has the least number of gas particles.Reducing the pressure on this equilibrium system results in the equilibrium position shifting to the side that has the most gas particles in order to increase the pressure
- if equal moles then no changes
Changes in Volume of Gaseous Equilibrium Systems
- a gas at reduced volume has a higher pressure, a gas at increased volume has a lower pressure.
- do same as pressure
Changes in Temperature
- Endothermic Equilibrium Systems
- Increasing the temperature of the equilibrium system will shift the equilibrium position to the side that does not include the energy term in order to reduce the temperature
- vice versa
- Exothermic Equilibrium Systems
Effect of a catalyst
catalyst does not affect the equilibrium state of a system. It only permits the system to attain its equilibrium state faster.
concentrations in equilibrium reactions
- products of the decomposition = initially 0, increase until = stable final concentration.
- concentration reactant initially large
- eventually arrives at some stable final concentration o products/reactants
- once the system reaches equilibrium, the concentrations or mole ratios are constant, the forward reaction rate = reverse reaction rate
Law of Chemical Equilibrium
- not dependent on initial concentrations but varies with temperature.
- describes the endpoint of a reversible reaction;
- use it to determine which reaction, either the forward or the reverse reaction, is favoured if we know the concentrations
interpreting K value
- If k > 1 = products are favoured at equilibrium.
- If 0 < k < 1 = reactants are favoured at equilibrium.
- Solids are not included in the K calculation.
Different K values
- Kc is used for the equilibrium constant using concentrations.
- Kp is used for the equilibrium constant using pressures.
- Ksp is used for the solubility product.
- Kw is used for the equilibrium constant for water.
- Ka is used for the acidity constant.
- Kb is used for the basicity constant.
Equilibrium Constant Applied to Solubility
- In order to have a chemical equilibrium in a solution containing a solid, you must have: a saturated solution
- an excess of non-dissolved solid in the solution
- a constant temperature
solubility of a substance
- mass of the substance can be dissolved in 1 of solution
- rate at which the solid dissolves is equal to the rate of precipitation
solids do not play a role
analyze Ksp value
- solution becomes more and more soluble as its Ksp increases.
- higher the value of K, the more a reaction tends towards the right.
- There must be ions in the mixture which can react together, formation of the precipitate depends on the nature of theions.
- The concentration of the solutions that are mixed must be high enough to give an ionic product which is higher than the Ksp of the precipitate.
- If the product of the [ions] is higher than the Ksp of the product, a precipitate will form.
chemicals that change colours within a specific pH range
H+ or the hydrogen ion = a proton,
- reaction of an acid with a base
- physical and chemical properties of the base and the acid disappear.
- hydrogen ions (H+) of the acid react with hydroxide ions (OH-) of the base to form water and a salt.
- becomes neutral (pH 7).
- The [OH-] is equal to the [H+]
- end point of the titration occurs when the indicator changes color
- equal quantities of hydrogen and hydroxide ions producing a neutral solution