Rates of reaction Flashcards
what does rate of a chemical reaction mean?
how fast reactants are changed into a product
slowest chemical reaction
rusting of iron
example of slow chemical reaction
-chemical weathering: acid rain damage to limestone buildings
example of moderate chemical reaction
-magnesium reacting with acid producing gentle bubbles
example of fast reaction
- burning
- explosions release lots of gas and are over in fraction of sec
- steeper the line on a graph…
- line becomes less steep…
- quickest reactions have…
- faster rate of reaction
- as reactant gets used up over time
- steepest line and becomes flat quickly
COLLISION THEORY: rate of reaction depends on?
- collision frequency of reacting particles
- enough energy transferred for successful collision
what does rate of reaction depend on?
- temp
- concentration/pressure
- surface area
- catalyst
how does increasing temp increase the rate?
- faster particles
- more frequent collisions
- enough energy
how does increasing concentration/ pressure increase the rate?
- more conc: more particles colliding in same volume
- more pressure: same number particles occupy smaller space
- more frequent collisions
how does increasing surface area increase the rate?
- breaking solid into smaller pieces increase SA:V
- same vol but more area
- more frequent collisions
how does increasing catalyst increase the rate?
example of biological catalyst
- decreases activation energy for reaction to occur
- provides alt. reaction pathway with lower activation energy
- enzyme
how to calculate the rate of a reaction?
amount of reactant used/formed/ time
give 3 different ways to use colour change to measure rate of reaction
- visual change: cloudy precipitate in transparent solution
- time how long mark thru solution disappears
- time how long solution loses or gains colour
why is observing a mark method to measure rates of reaction unreliable?
- different judgements
- can’t plot graph from results
explain how to use change in mass to measure rates of reaction which release gas?
what is the advantage and disadvantage?
- as gas released, mass loss shown on balance
- quicker change in reading, faster reaction
- measure at regular intervals to plot graph
- most accurate
- release gas into room
explain how to use volume of gas given off to measure rates of reaction which release gas?
what is an advantage and disadvantage?
- more gas released in gas syringe in given time, faster reaction
- measure at regular intervals and plot graph
- accurate to nearest cm3
- too vigorous blows plunger out of syringe
Mg and HCl react to produce H2 gas (PRACTICAL)
control variables
- add set vol of dilute HCL acid to flask on balance
- add Mg ribbon and plug flask with cotton
- start stopwatch and record mass at regular intervals
- plot table and work out mass loss for each to plot graph (time x-axis)(mass loss y-axis)
- repeat with more conc acid
- control variables: vol of acid, Mg ribbon
sodium thiosulfate and HCl produce a cloudy precipitate
control variable
disadvantage
- add set vol of dilute STS to flask on paper with black cross
- add dilute HCl and start stopwatch
- time how long black cross disappears thru sulfur precipitate
- repeat with different conc of either reactant at a time
- depth of liquid
- can’t plot graph
what is equalibrium?
what conditions does it need?
- forward and backward reaction cause no overall effect as concentrations of both are balanced and won’t change
- closed system so nothing gets in or not
if equilibrium lies to the right…
more conc of products
if equilibrium lies to the left…
more conc of reactants
are reversible reactions endothermic or exothermic?
explain thermal decomposition of hydrated copper sulfate
- endo and exo in opposite ways
- energy transferred from/to surroundings are equal
- heat blue hydrated copper sulfate crystals for white anhydrous copper sulfate powder –> endothermic
- add water to get blue back –> exothermic
what is Le Chatelier’s Principle?
- change condition of reversible reaction at equilibrium, system will try to counteract change
- temp
- pressure
- concentration
changing temp changes equilibrium
- decrease temp: moves exo direction,more heat, more products
- increase temp: moves endo direction, less heat, more products
changing pressure changes equilibrium
- increase: tries to reduce and moves where fewer gas molecules
- decrease: tries to increase and moves where more gas molecules
changing concentration of reactants changes equilibrium
increase: system reduces by making more products
decrease: system increases by making less products
