4.1-4.7 Flashcards
what is the ‘initial rate method’ for measuring rates of reaction
timing how long it takes to form a fixed amount of product
what is the ‘continuous method’ for measuring rates of reaction
the variation in the amount of reactant or product is followed with time
what can be measured for the ‘continuous method’ for measuring rates of reaction
the volume of gas
the change in mass
use a calorimeter
what’s the difference between the initial rate method and the continuous method for measuring rates of reaction
the initial rate method only gives an average rate of reaction but the continuous method allows you to see how rate changes with time
how can the rate of a reaction be increased
increase concentration of reactants increase pressure of gasses increase surface area of solids increase temperature add a catalyst
what is collision theory
particles must collide with a certain minimum energy and in a certain orientation before a reaction can take place
how can a rate of reaction be increased according to collision theory
increase the frequency of collisions (increase particle speed or number of particles)
increase the amount of successful collisions (increase energy of particles or lower the activation energy)
how does concentration change the rate of reaction
increasing concentration increases the number of particles. this increases the frequency of collisions so rate increases
how does pressure change the rate of reaction
increasing pressure increases the number of particles in a given volume for a gas. this increases the frequency of collision so rate increases
how does surface area change the rate of a reaction
increasing the surface area of a solid exposes more particles which increases the frequency of collisions so rate increases
how does temperature change the rate of a reaction
increasing temperature increases the average energy of the particles. this causes more successful collision so rate increases
how does a catalyst change the rate of reaction
adding a catalyst lowers the activation energy of the reaction. this increases the number of successful collisions so rate increases
why does rate of reaction decrease with time
the concentration of reactants decreases with time so there are less frequent collisions decreasing the rate of reaction
what’s a Boltzmann distribution graph
a graph of #particles against energy.
no particles have zero energy but some particles have very high energy
how does increasing temperature affect a Boltzmann distribution graph
the average energy increases and the curve becomes flatter because the spread of particles with certain energies increases. area under the curve stays constant
how does decreasing temperature affect a Boltzmann distribution graph
the average energy decreases and the curve gets more pointed as the spread of energies decreases
how can you find the number of particles with sufficient energy to react from a Boltzmann distribution graph
the area under the curve beyond the activation energy
describe how increasing temperature changes the rate of reaction considering a Boltzmann distribution graph
increasing temperature increases the proportion of particles with energy greater than the activation energy. the area beyond the activation energy on the graph increases
describe how using a catalyst changes the rate of reaction considering a Boltzmann distribution graph
the position of the activation energy on the graph moves to the left so the area beyond the activation energy increases. this corresponds to the number of particles that can successfully collide an react.
what is a homogenous catalyst
in the same physical state as the reactants
mostly occurs in solution
proceeds via an intermediate
what’s a heterogenous catalyst
different physical state than reactants
usually solids with a reaction taking place on its surface
benefits of catalysts
time is money lowers operating temp/press increase yield of exothermic reaction in reasonable amount of time saves energy reduces emissions allows for higher atom economy reactions
define dynamic equilibrium
the rate of the forward reaction equals the rate of the reverse reaction in a closed system. the concentration of products and reactants do not change
what is Le Chatelier’s principle
if dynamic equilibrium is disturbed by changing the conditions the position of equilibrium moves to counteract the change
how does the position of equilibrium change when the concentration of the reactants is decreased
the position of equilibrium will move towards the reactants (left side of reaction). this is to produce more reactants to counteract the decrease
how does the position of equilibrium change when pressure is increased
the position or equilibrium will move to the side of the reaction with the fewest moles of gas
how does the position of equilibrium change when temperature is increased
it moves in the direction of the endothermic reaction. this counteracts the change by absorbing the energy
how do catalysts affect the equilibrium position
they increase the rates of the forward and reverse reaction equally so catalyst do not affect the position of equilibrium, only how quickly it is reached
in industry, why are high temperatures used if the forward reaction is exothermic
it is a compromise. a lower temperature means a slower rate of reaction. using a high temperature is a compromise for the yield of the product and the rate that it is produced
in industry, why are extremely high pressures not used if the products have fewer moles of gas
using high pressures is dangerous and extremely costly. using a lower pressure is a compromise between yield, rate and cost
what is the equilibrium constant
a measure of the position of equilibrium. the magnitude of the constant indicates whether there are more reactants or products when in equilibrium. its constant if temperature is constant
what affects the equilibrium constant and what doesn’t
its not affected by pressure or catalysts
its only affected by concentration and temperature
what values of the equilibrium constant (Kc) indicate the position of equilibrium
if Kc > 1 the position lies to the right
if Kc < 1 the position lies to the left
what is a homogenous reaction
all the reactants and products are in the same physical state so all of them appear in the formula for the equilibrium constant
what is a heterogenous reaction
the reactants and products are in different physical states so only the gaseous and aqueous substances appear in the formula for the equilibrium constant
