4.1-4.7

Question 1

what is the ‘initial rate method’ for measuring rates of reaction

Answer 1

timing how long it takes to form a fixed amount of product

Question 2

what is the ‘continuous method’ for measuring rates of reaction

Answer 2

the variation in the amount of reactant or product is followed with time

Question 3

what can be measured for the ‘continuous method’ for measuring rates of reaction

Answer 3

the volume of gas
the change in mass
use a calorimeter

Question 4

what’s the difference between the initial rate method and the continuous method for measuring rates of reaction

Answer 4

the initial rate method only gives an average rate of reaction but the continuous method allows you to see how rate changes with time

Question 5

how can the rate of a reaction be increased

Answer 5

increase concentration of reactants
increase pressure of gasses
increase surface area of solids
increase temperature
add a catalyst

Question 6

what is collision theory

Answer 6

particles must collide with a certain minimum energy and in a certain orientation before a reaction can take place

Question 7

how can a rate of reaction be increased according to collision theory

Answer 7

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)

Question 8

how does concentration change the rate of reaction

Answer 8

increasing concentration increases the number of particles. this increases the frequency of collisions so rate increases

Question 9

how does pressure change the rate of reaction

Answer 9

increasing pressure increases the number of particles in a given volume for a gas. this increases the frequency of collision so rate increases

Question 10

how does surface area change the rate of a reaction

Answer 10

increasing the surface area of a solid exposes more particles which increases the frequency of collisions so rate increases

Question 11

how does temperature change the rate of a reaction

Answer 11

increasing temperature increases the average energy of the particles. this causes more successful collision so rate increases

Question 12

how does a catalyst change the rate of reaction

Answer 12

adding a catalyst lowers the activation energy of the reaction. this increases the number of successful collisions so rate increases

Question 13

why does rate of reaction decrease with time

Answer 13

the concentration of reactants decreases with time so there are less frequent collisions decreasing the rate of reaction

Question 14

what’s a Boltzmann distribution graph

Answer 14

a graph of #particles against energy.

no particles have zero energy but some particles have very high energy

Question 15

how does increasing temperature affect a Boltzmann distribution graph

Answer 15

the average energy increases and the curve becomes flatter because the spread of particles with certain energies increases. area under the curve stays constant

Question 16

how does decreasing temperature affect a Boltzmann distribution graph

Answer 16

the average energy decreases and the curve gets more pointed as the spread of energies decreases

Question 17

how can you find the number of particles with sufficient energy to react from a Boltzmann distribution graph

Answer 17

the area under the curve beyond the activation energy

Question 18

describe how increasing temperature changes the rate of reaction considering a Boltzmann distribution graph

Answer 18

increasing temperature increases the proportion of particles with energy greater than the activation energy. the area beyond the activation energy on the graph increases

Question 19

describe how using a catalyst changes the rate of reaction considering a Boltzmann distribution graph

Answer 19

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.

Question 20

what is a homogenous catalyst

Answer 20

in the same physical state as the reactants
mostly occurs in solution
proceeds via an intermediate

Question 21

what’s a heterogenous catalyst

Answer 21

different physical state than reactants

usually solids with a reaction taking place on its surface

Question 22

benefits of catalysts

Answer 22

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

Question 23

define dynamic equilibrium

Answer 23

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

Question 24

what is Le Chatelier’s principle

Answer 24

if dynamic equilibrium is disturbed by changing the conditions the position of equilibrium moves to counteract the change

Question 25

how does the position of equilibrium change when the concentration of the reactants is decreased

Answer 25

the position of equilibrium will move towards the reactants (left side of reaction). this is to produce more reactants to counteract the decrease

Question 26

how does the position of equilibrium change when pressure is increased

Answer 26

the position or equilibrium will move to the side of the reaction with the fewest moles of gas

Question 27

how does the position of equilibrium change when temperature is increased

Answer 27

it moves in the direction of the endothermic reaction. this counteracts the change by absorbing the energy

Question 28

how do catalysts affect the equilibrium position

Answer 28

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

Question 29

in industry, why are high temperatures used if the forward reaction is exothermic

Answer 29

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

Question 30

in industry, why are extremely high pressures not used if the products have fewer moles of gas

Answer 30

using high pressures is dangerous and extremely costly. using a lower pressure is a compromise between yield, rate and cost

Question 31

what is the equilibrium constant

Answer 31

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

Question 32

what affects the equilibrium constant and what doesn’t

Answer 32

its not affected by pressure or catalysts

its only affected by concentration and temperature

Question 33

what values of the equilibrium constant (Kc) indicate the position of equilibrium

Answer 33

if Kc > 1 the position lies to the right

if Kc < 1 the position lies to the left

Question 34

what is a homogenous reaction

Answer 34

all the reactants and products are in the same physical state so all of them appear in the formula for the equilibrium constant

Question 35

what is a heterogenous reaction

Answer 35

the reactants and products are in different physical states so only the gaseous and aqueous substances appear in the formula for the equilibrium constant