Chapter 10 reaction rates Flashcards
What is the rate of a chemical reaction
- 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
What is the forula for the rate of reaction
change in concentration/time
Describe the graph for the rate of reaction
- 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
How are factors that alter the rate of a chemical reaction
- concntration - pressure when reactants are gases
- temperature
- catalyst
- surface area of solid reactants
What does the collission theory state
- two reacting particles must collide for a reaction to occur
What are the two conditions for a collision to be succesful
- the particles have to collide with the correct orientation
- particles have sufficient eenergy to overcome the activation energy barrier of the reaction
How does increasing the concentration affect the rate of a reaction
- 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
How increaing the pressure affect the rate of a reaction
- 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
What are method for following the progree of a reaction
- monitoring removal (decrease in concentration) of a reactant
- following the formation (increae in concentration) of a product
Describe how you can monitor reactions that produce gas
- mointoring volume of gas produced at regular time intervals using gas collection
- monitoring the loss of mas of reactants using a balance
What is a catalyst
- 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
What is a homogenous catalyst
- same physical state as the reactants
- react to form an indetermediate that break down to give products and regenerates the catalyst
What are two example of use of homogenous catalysts
- making esters with sulfuric acid as a catalyst
- liquid state
- oxone depletions chlorine radical a a catalyst
- gaseous state
What is a heterogenous catalyst
- 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
What are example of reactions using heterogenous catalysts
- making ammonia - iron
- hydrogenation of alkenes - nickels
Why are catalyst beneficial for economies
- 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
What are the feature of a boltzman distribution graphs
- 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
What will happen to the boltsman distibution graph at higher temperatures
- activation energy is greater
- peak shift to the right and lowers
Describe the effect of temperature on the rate of reaction using maxwell distribution graph
- 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
Describe the change to the maxwell distribution graph to the addition of a catalyst
- shifts to the left
Describe the effect of a catlayst on the rate of reaction using maxwell distribution graph
- 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
What is a reversible reaction
- both forward and reverse reaction will take place
What are the features of dynamic equilibrium
- 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
What is a closed system
- isolated from its surroundings so the temperature, pressure and concentration os reactants and products are unaffected by outide influences
What does the position of equlibrium indicate
- the extent of the reaction
- if the reversible reaction if the temperature, pressure for reactions involoving gases change the position of equilibrium may change
What does le chatliers principle state
- when a system is in equilibrium is subjected to an external change the system readjust itself to minimise the effect of that change
What happens to the positition of equilbrium if concentrations of reactants increases
- shifts to the side of the products
What happens to the position of equilibrium if the temperature increases
- favour the endothermic side
What happens to the position of equilibrium if pressure increases
- shifts to the side where there less moles of gas
What effect of a cataylst have on equilbrium
- does not change the position of equilibrium
- speed up the rate of forward and backward reactions equally
What is the compromise between industries and postiion of equilirbium
- high pressures - expensive and dangerous
- low temperature - slow rate of reaction
What is an equilibrium constant
- 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
What does the Kc value state about the position of equilbrium
- 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
