rate and extent of reaction Flashcards
how can you measure ROR?
measuring the quantity of a reactant used or the quantity of a product formed over time
equation to determine mean rate of reaction using reactant
mean rate = quantity of reactant used divided by time
equation to determine mean rate of reaction using a product
mean rate = quantity of product formed divided by time
how do you measure the amount of reactant or product in a reaction?
mass (g) or volume (cm3)
what are the units for rate of reaction?
g/s using mass or cm3/s using volume
what are the units for rate using moles?
mol/s
how can you measure rate of reaction from a graph at a specific time?
draw a tangent and determine the gradient
when drawing a tangent, how should the ruler be positioned on the graph?
place the ruler on the curve at the point where you want to know the slope. the space between the ruler and the curve should be equal on both sides of the point.
how do you calculate the mean rate of reaction from a graph?
rate (gradient) = change in y divided by change in x
calculate the mean rate of reaction that produces 52cm3 of gas in 2 minutes
52 divided by 2 = 26cm3/minute
what does the steepness of the slope on a rate graph tell you?
how fast the reaction is. steeper the line, faster the reaction.
how can you tell from a rate graph that the reaction has finished.
the graph becomes flat
how can you measure rate?
loss of mass of reactants or volume of a gas produced or time for a solution to become cloudy or coloured
what piece of equipment can you use to measure volume of gas made?
gas syringe or ‘over water’ using an upturned measuring cylinder in a water trough
what factors can affect the rate of reaction?
concentration
pressure
surface area
temperature
catalyst
what is collision theory?
reactants must collide with enough energy the overcome the activation energy
what is activation energy?
the minimum amount of energy that particles must have to react.
what must particles have when they collide?
activation energy
what does increasing temperature do in terms of collision?
rate increases, because particles move faster so there are more frequent collisions and more particles are colliding with energy greater than the activation energy
what does increasing concentration do in terms of collisions?
more particles in a given volume therefore more frequent collisions
how can you increase the surface area of a solid?
break up the solid into smaller pieces
what does increasing pressure do in terms of collision?
same number of particles in a smaller volume so more crowded, frequency of collisions increases.
what is a catalyst?
a substance which increases rate of chemical reactions but are not used up during the reaction, different reactions need different catalysts
example of a biological catalyst?
an enzyme
how do catalysts increase the rate of reaction
provide a different pathway with a lower activation energy.
are catalysts included in chemical equations
no
what is a reversible reaction?
the products of the reaction can react to produce the original reactants
why does the amount of products and reactant remain the same at equilibrium?
the rate of forward reaction is equal to the rate of backward reaction so the concentrations of the products and reactant remain constant.
how does a reaction reach equilibrium?
when a reversible reaction occurs in a closed system and the forward and reverse reaction happen at the same rate
what is a closed system?
when it is sealed, products and reactants cannot enter or leave
an equation to show the reversible reaction when ammonium chloride is heated
. >heat
amonium chloride<=>ammonia+hydrogen chloride
. <cool
how can you change the direction of a reversible reaction?
by changing the conditions of temp, pressure, or concentration
if a reversible reaction is exothermic in one direction, what will it be in the opposite direction?
endothermic
what is the amount of energy like in both directions in a reversible reaction?
the same
what is equilibrium?
when forward and reverse reactions occur at exactly the same rate (when in a closed system so reactants and products cant escape from the apparatus)
what is Le Chateliers principle?
at equilibrium, if the conditions change it will shift to oppose these changes. (to get back to equilibria)
what happens if concentration of one of the reactants or products is changed?
the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again
what happens if concentration of reactants increases?
more products will be made until the equilibrium is reached again
what happens if the concentration of the products are decreased?
more reactants will react until equilibrium is reached again
what happens if temperature is increased?
the equilibrium will always move in the endothermic direction
what happens if temperature is decreased?
the equilibrium will always move in the exothermic direction
what happens if temperature is increased for an endothermic reaction?
the amount of products will increase (it will want to cool back down so favours the endothermic reaction)
what happens if temperature is decreased for an endothermic reaction?
the amount of products will decrease (it will want to heat up so it favours the exothermic reaction)
what happens if the temperature is decreased for an exothermic reaction?
the amount of products will increase (it will want to heat up so it favours the exothermic reaction)
what happens if temperature is increased for an exothermic reaction?
the amount of products will decrease (it will want to heat up so favours the endo thermic reaction)
if a change in pressure occurs what do you look at?
the number of GASEOUS moles on reactants vs products
e.g: N2(g) + 3H2(g) <=> 2NH3(g)
there are 4 moles of gas on the reactants side. there are 2 moles of gas on the products side.
what happens if pressure is increased in an equilibrium?
equilibrium will shift towards the side with less gaseous moles
what happens if pressure is decreased in an equilibrium?
equilibrium will shift towards the side with more gaseous moles
what affect does pressure have if the same number of molecules in the reactant and products
no effect
what affect does the catalyst have on the position of the equilibrium?
none, it speeds up the rate of both the forward and backwards reaction equally
