c8 rates of reaction Flashcards
mean rate of reaction
(reactant)
quantity of reactant used/time taken
mean rate of reaction (product)
quantity of product formed/time taken
unit of rate of reaction
g/s or cm3/s
when plotting a graph for rate of reaction what goes in the x-axis?
time
when do you draw a tangent on a specific point and calculate the gradient of the tangent?
to measure the rate of reaction at a specific time
factors which affect the rates of chemical reactions include:
-the concentration of reactants in the solution
-the pressure of reacting gasses
-the surface area of solid reactants
-the temperature
-presence of a catalyst
as you increase the temperature
the rate of reaction increases but same amount of products produced at the end
what is concentration?
-increasing concentration increases rate
the number of particles dissolved in a given volume of solvent
what is pressure
increased pressure=increased number of particles
a measurement of the number of particles in a given volume of gas
is the surface area of a block or powder of that block greater?
powder surface area greater
highest rate of reaction means
steepest gradient
what does collision explain?
how various factors affect the rates of reactions
chemical reactions can only occur when
reacting particles collide with each other and with sufficient energy
what is the activation energy?
the minimum amount of energy that particles must have to react is called the activation energy
what does increasing the concentration of reactants in solution, the pressure of reacting gases and the surface area of solid reactants increase?
the frequency of collisions so increases the rate of reaction
increasing the temperature increases the frequence of collisions. What does this do?
this makes the collisions more energetic,and so increases the rate of reaction
increasing temperature
particles have more kinetic energy
move faster
more collisions per second
collide with more energy
larger surface area (lump cut up into smaller parts)
more particles exposed to other reactants more frequent collisions
catalysts
reduce the amount of energy needed for particles to have a successful collision
enzymes act as catalysts in?
biological systems
what are reversible reactions?
example: A + B ⇌C + D
reactions where the products of the reaction can react to produce the original reactions
the direction of reversible reactions can be changed by?
changing the conditions
For example: heat
ammonium chloride ⇌ ammonia + hydrogen chloride cool
if a reversible reaction is exothermic in one direction, what is it in the opposite direction?
endothermic
in reversible reactions, one reaction is exothermic and the other is endothermic so the same amount of energy is transferred in each case.
give an example
endothermic
ammonium chloride ⇌ ammonia + hydrogen chloride exothermic
when a reversible reaction occurs in apparatus which prevents the escape of reactants and products, when is equilibrium reached?
when the forward and reverse reactions occur exactly at the same rate
dynamic equilibrium
in a reversible reaction,rate of the forward reaction is equal o the rate of the backward reaction ina closed system
three conditions affect the rate of reaction:
-temperature
-pressure
-concentration
what is le chatlier’s principle?
When a reaction has reached dynamic equilibrium and a change occurs the position of equilibrium will move to counteract the change. This concept is known as Le Chatelier’s principle.
required practical:the disappearing cross reaction
sodium thiosulfate solution + hcl–>sulfur (solid). what does sulfur do to the solution?
sulfur makes the solution go cloudy (turbidity)
steps for disappearing cross reaction:
-use a measuring cylinder put 10cm3 of sodium thiosulfate in conical flask
-place the conical flask onto a printed black cross
-add 10cm3 of hydrochloric acid into the conical flask
-swirl solution , start a stopwatch
after some time, what happens to the solution?
it turns cloudy, stop clock when cross no longer visible
repeat again using?
lower concentrations of sodium thiosulfate
repeat the whole experiment and ?
calculate the mean with no anomalies included
reproducibility
can be repeated with different people or equipment but still same result
what is the problem with this experiment?
different eyesights , people might see cross for longer however same size printed cross helps solve this
