rates of reaction Flashcards
investigating effect of surface area on rate - hydrochloric acid and marble chips
- CO2 is produced in the reaction so take readings of the gas volume at even intervals and plot on a graph to work out the RoR
- repeat for different sizes of marble chips annd calcium powder to compare the effect of surface area to the RoR
what ways can you measure the rate of reaction? (2)
- rate which products are made
- rate at which reactants are used up
what factors affect rate of reaction? (5)
- concentration (of solutions)
- temperature
- surface area (solids)
- catalyst (presence/absence)
- pressure (gases)
what is a catalyst?
- a substance that speeds up the rate of reaction without altering the products of reaction
- catalyst remains uchanged chemically and in mass at the end of the reaction (does’t get used up)
how do catalysts work?
provide an alterative reaction pathway with a lower activation energy needed for a reaction to take place
collision theory
rate of reaction depends on…
- collision frequency of reacting particles (proability of a sucesful collision increase)
- the energy transferred during a collsion (have to collide with enough energy for a reaction to take place)
how much energy do particles need for a succesful collision?
collision must be equal or greater than the activation energy so that bonds can be broken between reactant particles
how does increased surface area increase rate of reaction?
greater area of contact for the other reactant to collide on so there will be more frequent collisions which means a higher likelyhood of succesful collisions leading to a faster rate of reaction
how does a higher temp lead to a faster rate of reaction?
higher temp will increase the thermal energy of the particles meaning:
- the particles move faster and much more frequently
- more collisions have energy that exceeds the activation energy so there are more succesful collisions therefore a faster RoR
how does a higher pressure/concentration lead to a faster rate of reaction ?
higher pressure/concentration means there will be more particles in a certain area which will icrease frequency of collisions leading to a higher RoR
why do rate of reaction graphs level off?
reaction has finished because all reactants have been used up
what are enzymes?
- biological catalysts
- catalyse/ speed up the chemical reaction inside living organisms eg to digestion, respiration and photosythesis
how are enzymes used in alcohol production?
enzymes (biological catalysts) from yeast cells are used in the fermentation process used to make alcoholic drinks
rate of reaction equations (2)
RoR = change in amount of reactant or a product / time
RoR = number of succesful reactions/ time
which variables can be measured?
CORE PRACTICAL: calcium carbonate and hydrochloric acid
- mass loss of system
- volume of CO2 produced
- increase in pH
- decrease in concentration of acid
which variables can be measured?
CORE PRACTICAL: sodium thisulfate and hydrochloric acid
time it takes to produce enough sulfur to block view of a cross
which variables can be measured?
decomposition of hydroge peroxide
- volume of O2 produced
- mass loss of system
which variables can be measured?
metal and acid
- mass loss
- volume of H2 produced
- change in pH
- dcrease in concentratio of acid
how does the rate of reaction change as the reaction progresses and why?
- RoR is highest at start because there is the highest concentration of reactants
- as reaction goes on, it slows down
what is rate of reactio shown by in a graph?
the steepness (gradient) of the curve
what does an increase of 10°C do to the rate of reaction?
doubles the RoR
what is the activation energy?
the minimum amount of energy required to get a reaction started/ particles need to collide with for it to be a succesful collision
