reactivity 2.2
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describe a graph Time X amount of reactant (concentration of reactant)
decay curve
describe a graph Time X amount of product
increase, exponential curve
explain the appearance of the graphs of amount of reactnat or product against time
shapes of th graphs due to the change in amount of reactant as the eaction proceeds, at start of reaction, rate is at its max= initial rate, since the amount of reactants is at their highest level, numb of collisions between particles is at its max, initially rate of consumption of reactant and rate of formation of product at their fastest
explaining time Vs concentration graph excess and limiting
if one of reactants is in excess, excess amount of this substance will remain even after reaction has ended , substance that is limiting will have been consumed
how do you calculate rate of reaction from a time Vs conc graph
gradient= change in amount/ change in time draw a gradient line at. tangent from the curve, initial line has to go through 0,0
what is the difference between the initial rate of reaction and the avergae rate of reaction
initial rate is faster than average
how would the difference between initial rate of reaction and the average rate of reaction change with increasing time of experiment
as time increases the difference between initial and avergae rate increases
what is the relationship between the initial rate of reaction and the conc of acid
porportional, higher conc of acid there is an increase in rate
what are ways you can measure rate of reaction in a reaction which one of the reactants is a solid and one of the products is a gas
• gas syringe, measures production of gas product • displacement over water, also collects production of gas product graph would be an exponential curve which eventually reaches a plateau as time increases • change in mass of reactant using a balance and cotton wool on top of flask (allows gas products to escape, but not other reactnants or products), graph would be an exponential decrease
how would you measure rate of reaction in a reaction which produces a colored precipitate
• time taken for X to disappear (only get 1 data point) 2.use colorometer (use complementary colour to solution)
activation energy in a graph is
difference between reactants and top peak
enthalpy chage in a graph is
difference in eenrgy between reactants and products
why is it than even though a reaction is feasible it may not occur spontaneuosly
because molecules may not have sufficient energy to overcome activation energy recquire to break bonds
for a reaction to occur what are the 3 recquirment reactant particles must fulfill
-they must collide -they must have energy greater than or equal to the activation energy -they must meet the correct geometrical alignment
how does stirring affect rate of reaction
increases chance of collision and also reduces localised variation in conc
how does light affect rate of reaction
some reactins are photochemical and rate of reaction is ncreased by increasing the light intensity more partiles have enough activation energy needed to break bonds, start reaction
concentration/ pressure and rate of reaction
increase conc= increase rate increase conc= more particles in a given volume= greater chance of successful collision for gases increasing pressure= particles closer together= greater chance of successful collision
surface area and rate
bigger surface area= bigger rate = increases frequency of colisions= increase rate
temperature and rate
increase in temp= inrease avergae KE of particles in a system= increase speed of particles • particles move faster= collide more frequently= increase rate • more particles have energy grater than or equal to activation energy
describe the Maxwell Boltzman distribution
for an ideal gas system distribution of particles with different energies -no molecules at zero energy -few molecules at high energy -no max energy value= asymptote never reachs Y=0 - peak= mean KE of particles particles before the line of activation energy dont react, particles after Ea react as they have kinetic energy equal or greater than Ea , break bonds and react area under graph represents the amount of particles x axis= kinetic energy y axis= numb of molecules
explain what happens to maxwell boltzman (kinetic energy in x-axis) distribution graph when: increase temp
peak of the graph is more towards the right (higher KE), graph is in general shorter, as more particles have higher KE and same numebr of particles remain more particles have kinetic energy greater or equal to Ea, thus increase rate
describe the graph of velocity vs numb of molecules at same temperatures
at same temp= same average KE however particles have different speeds since size of particles change smaller particles (smaller Mr)= bigger speeds KE= 1/2mVˆ2
catalysts and rate
+ catalyst= higher rate catalysts decrease rate of reaction in a maxwell distribution graph, graph is the same onyl thing that change is line for Ea which is brought more towards Left lower Ea= more particles have KE greater or equal to Ea, means higher rate single step reaction broken down into severl steps
rate
1/ time