Chapter 10 reaction rates

Question 1

What is the rate of a chemical reaction

Answer 1

• measures how fast a reactant is being used up or how fast a product is being formed
• defined as the cahnge in conentration of a reactant of product in a given time

Question 2

What is the forula for the rate of reaction

Answer 2

change in concentration/time

Question 3

Describe the graph for the rate of reaction

Answer 3

• rate of reaction is fastest at the start of a reaction as each of the reactant is at it’s highest concentration - curve is steep
• the rate of reaction slows down as the reaction preoceeds because the reactants are being used up and their concentrations decrease
• once one of the reactant has been completley ued up the concnetration stop changing and the rate of reaction is zero - line plateus

Question 4

How are factors that alter the rate of a chemical reaction

Answer 4

• concntration - pressure when reactants are gases
• temperature
• catalyst
• surface area of solid reactants

Question 5

What does the collission theory state

Answer 5

• two reacting particles must collide for a reaction to occur

Question 6

What are the two conditions for a collision to be succesful

Answer 6

• the particles have to collide with the correct orientation
• particles have sufficient eenergy to overcome the activation energy barrier of the reaction

Question 7

How does increasing the concentration affect the rate of a reaction

Answer 7

• rate of reaction increases
• an increase in concentration inceaes the number of particles in the same volume
• particles are closer together and collide more frequently
• in a given period of time more effective collissions

Question 8

How increaing the pressure affect the rate of a reaction

Answer 8

• gas is compressed into a smaller volume pressure increased
• rate of reaction increases
• concentration of gas molecules increases as same number of gas molecule occupy a smaller volume
• gas molecules are closer together and collide more frequently leading to more successful colliions in the same time

Question 9

What are method for following the progree of a reaction

Answer 9

• monitoring removal (decrease in concentration) of a reactant
• following the formation (increae in concentration) of a product

Question 10

Describe how you can monitor reactions that produce gas

Answer 10

• mointoring volume of gas produced at regular time intervals using gas collection
• monitoring the loss of mas of reactants using a balance

Question 11

What is a catalyst

Answer 11

• substance that changes the rate of a chemical reaction without undergoing any permanent changes itself
• may react with a reactant to from an intermediate of provide a surface for reaction can take place
• increases rate of a chemical reaction
• providing an alternative reaction pathway of lowering the activation energy

Question 12

What is a homogenous catalyst

Answer 12

• same physical state as the reactants
• react to form an indetermediate that break down to give products and regenerates the catalyst

Question 13

What are two example of use of homogenous catalysts

Answer 13

• making esters with sulfuric acid as a catalyst
• liquid state
• oxone depletions chlorine radical a a catalyst
• gaseous state

Question 14

What is a heterogenous catalyst

Answer 14

• different phyical states from the reactants
• usually solid in contact of gasous reactant
• reactant molecules are absorbed onto the surface of the catalyst where the reaction take place
• after reavtion product molecules the surface of the catalyst being desorption

Question 15

What are example of reactions using heterogenous catalysts

Answer 15

• making ammonia - iron
• hydrogenation of alkenes - nickels

Question 16

Why are catalyst beneficial for economies

Answer 16

• increate the rate of reaction by lowering the activation energy. this then reduces the temperature needed fro the process and the energy requirements
• less energy is requires less electricity of fossil fuels is needed
• outweigh the costs and increases profatability by producing products faster
• higher atom economies and fewer pollutants

Question 17

What are the feature of a boltzman distribution graphs

Answer 17

• no molecules have zero energy the curve starts at the progom
• the area under the curve is equal to the total number of molecules
• there is no maximum energy for a molecule the curve does not meet the x axis at high energy the curve would need to reach infinite energy to meet x axis

Question 18

What will happen to the boltsman distibution graph at higher temperatures

Answer 18

• activation energy is greater
• peak shift to the right and lowers

Question 19

Describe the effect of temperature on the rate of reaction using maxwell distribution graph

Answer 19

• more molecules have an energy greater than or equal to the activation energy
• therefore a greater proportion of colliions will lead to a reaction increasing the rate of a reaction
• colliions will also be more frequent a the molecules are moving faster but the increased energy of the molecules i much more important than the inceased frequency of collisions

Question 20

Describe the change to the maxwell distribution graph to the addition of a catalyst

Answer 20

• shifts to the left

Question 21

Describe the effect of a catlayst on the rate of reaction using maxwell distribution graph

Answer 21

• catalyst provides an alternative reaction route with a lower activation energy
• greater propoertion of molecules have an energy equal to or greater than the lower activation energy
• on collission more molecules will react to form products
• the result is an increase in the rate of a reaction

Question 22

What is a reversible reaction

Answer 22

• both forward and reverse reaction will take place

Question 23

What are the features of dynamic equilibrium

Answer 23

• rate of forward reaction is equal to the rate of reverse reaction
• the concnetrations of reactants and products do not change
• system must be closed

Question 24

What is a closed system

Answer 24

• isolated from its surroundings so the temperature, pressure and concentration os reactants and products are unaffected by outide influences

Question 25

What does the position of equlibrium indicate

Answer 25

* the extent of the reaction * if the reversible reaction if the temperature, pressure for reactions involoving gases change the position of equilibrium may change

Question 26

What does le chatliers principle state

Answer 26

* when a system is in equilibrium is subjected to an external change the system readjust itself to minimise the effect of that change

Question 27

What happens to the positition of equilbrium if concentrations of reactants increases

Answer 27

* shifts to the side of the products

Question 28

What happens to the position of equilibrium if the temperature increases

Answer 28

* favour the endothermic side

Question 29

What happens to the position of equilibrium if pressure increases

Answer 29

* shifts to the side where there less moles of gas

Question 30

What effect of a cataylst have on equilbrium

Answer 30

* does not change the position of equilibrium * speed up the rate of forward and backward reactions equally

Question 31

What is the compromise between industries and postiion of equilirbium

Answer 31

* high pressures - expensive and dangerous * low temperature - slow rate of reaction

Question 32

What is an equilibrium constant

Answer 32

* provides an actual position of equilbrium * the magnitude of an equilbrium constant indicated wethere there are more reactants or more products in an equilbrium system

Question 33

What does the Kc value state about the position of equilbrium

Answer 33

* Kc value of 1 - position of equilbrium is halfway between reactants and products * Kc >1 position of equilbrium is towards product * Kc<1 posiftion of equilhrium is towards the reactants * larger the value of Kc he further the poition of equilbrium lies to the rigt hang side and greater concentrations of products compared to the reactants