Principles of chemistry - SPEC Flashcards
WHAT IS THE DIFFERENCE BETWEEN A PURE SUBSTANCE AND A MIXTURE IN RELATION TO ITS BOILING POINTS
pure - boils and melts at fixed temps
mixture - may melt or boil over a range of temps
what is the equation for the reversible reaction of the thermal decomposition of ammonium chloride
describe the reversible reaction of thermal decomposition of ammonium chloride
- heating ammonium chloride produces ammonia and hydrogen chloride gas
- as the hot gases cool down they recombine to form solid ammonium chloride
describe the reversible reaction of the dehydrtion of hydrated copper(II) sulfate
- when anhydrous copper sulfate is added to water, it turns blue and heat is given off
- when hydrated copper(II) sulfate is heated, the blue crystals lose their water and turn into a white powder and a clear colourless liquid (water)
what is one common reversible reaction
the dehydration of hydrated salts
when is a reaction in a state of equilibrium
when the rate of the forward reaction equals the rate of the reverse reaction
why is equilibrium dynamic
because the molecules on the left and right are constantly changing into each other at the same rate
therefore the concentration on reactants and products remains constant
what condition is needed to obtain dynamic equilibrium
it needs to occur in a closed system so that none of the participating chemicals can leave the vessel
describe how equilibrium is achieved
- at the beginning only the reactants are present so the rate of the forwards reaction is at its highest, since their concentration is at its highest
- as the reaction proceeds the concentration of reactants will gradually decrease so the rate of the forwards reaction will decrease
- and vice versa for the backwards reaction
- the rates of the reactions will eventually become equal and will stay that way
draw a graph of dynamic equilibrium being achieved
what are the two characteristics of a reaction at dynamic equilibrium
- the forward and backwards reactions occur at the same time
- the concentrations of reactants and products remain constant
what is the fundamental principle for dynamic equilibrium
when a change is made to the conditions of a system at equilibrium, it automatically moves to oppose the changes
what direction will the equilibrium move in after an increase in temperature
moves in the endothermic direction
(because it wants to get colder - in an endothermic reaction it absorbs the heat energy so IT gets colder)
if the equilibrium shifts LEFT, what does this mean for the concentration of the products and reactants
the concentration of the reactants INCREASES
eg for this reaction, a left shift will cause the mixture to become more dark brown in colour, because more ICl is produced
what direction will the equilibrium move in after an increase in pressure
shift in the direction that has the least number of GAS moles
to decrease the pressure again
what effect does a catalyst have on equilibrium
- it does not affect its equilibrium position
- it increases the rate at which equilibrium is achieved (because it increases the rate at which both the forward and the backward reaction is achieved)
