rates of reaction Flashcards
topic 7 - rates of reaction and energy changes
Core Practical: Investigate the effects of changing the conditions
of a reaction on the rates of chemical reactions by:
a) measuring the production of a gas (in the reaction
between hydrochloric acid and marble chips)
how to investigate the effect of surface area on rate using marble chips and hydrochloric acid
- set up apparatus
- measure volume of gas produced using a gas syringe
- take readings at regular time intervals and record results in a table
- plot graph
a) time on x-axis
b) volume on y-axis
- repeat experiment with exactly the same volume and concentration of acid and exactly the same mass of marble chips but with the powder more crunched up
- then repeat with the same mass of powdered chalk
* important your system is airtight so no gas escapes
* marble and chalk are both made up of calcium carbonate
Core Practical: Investigate the effects of changing the conditions
of a reaction on the rates of chemical reactions by:
a) measuring the production of a gas (in the reaction
between hydrochloric acid and marble chips)
what does the apparatus look like
conical flask attached to syringe
in the conical flask there is co2 gas and dilute HCL with marble chips (CaCO3)
(marble and chalk are both made of calcium carbonate)
Core Practical: Investigate the effects of changing the conditions
of a reaction on the rates of chemical reactions by:
b) observing a colour change (in the reaction between
sodium thiosulfate and hydrochloric acid)
- measure fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder
- use a water bath to gently heat both solution to the desired temperature before you mix them
- mix solutions in a conical flask
- place flask over a black mark on a piece of paper
- watch the black mark disappear through the cloudy, yellow sulfur and time how long it takes to go
- the reaction is repeated with different temperatures
- can use your results to measure what effect changing the temperature has on the rate of reaction
a) shorter length of time for mark to be gone = faster rate
Core Practical: Investigate the effects of changing the conditions
of a reaction on the rates of chemical reactions by
b) observing a colour change (in the reaction between
sodium thiosulfate and hydrochloric acid)
what should be controlled in this experiment
depth and volumes of liquid must be kept the same each time
concentrations of the solutions
why do we use sodium thiosulfate and hydrochloric acid
are both clear, colourless solutions that react together to form a yellow precipitate of sulfur
Suggest practical methods for determining the rate of a given
reaction
- measuring volume of gas given off by a reaction over time
- measuring loss of mass of a reaction over time when a gas is produced
- measuring amount of light that passes through a reaction mixture (as a precipitate forms) over time - can be done by inspection or using a light sensor and data logger
explain how reactions occur when particles collide
reactions happen if particles collide with enough energy to react
explain that rates of reaction are increased when the frequency of collisions increases
collision frequency of reacting particles - more successful collisions = faster reaction
explain that rates of reaction is increased by energy of collisions being increased
energy transferred during a collision
minimum energy that particles need to react when they collide = activation energy, particles need to collide with at least the activation energy for the collision to be successful
Explain the effects on rates of reaction of changes in
temperature
- temperature is increased the particles move faster and so they have more collisions
- higher temperatures increase energy of collisions since particles are moving faster (reactions only happen if particles collide with enough energy)
- meaning that at higher temperatures there will be more successful collisions
- so increasing rate of reaction
Explain the effects on rates of reaction of changes in concentration / pressure (gases)
- means there are more particles of reactant in the same volume so collisions are more likely and rate increases
- in a gas increasing the pressure means particles are more crowded so frequency of collisions between particles will increase so rate increases
Explain the effects on rates of reaction of changes in surface area to volume ratio of a solid
- if one reactant is solid breaking it into smaller pieces will increase its surface to volume ratio
- the particles around it will have more area to work on so frequency of collisions will increase
- larger surface area to volume ratio makes rate of reaction faster
how to interpret graphs
- if its a curve do a tangent
- gradient = change in y / change in x
- gradient = rate of reaction
- steeper gradient = faster rate
describe a catalyst
- a substance that speeds up the rate of a reaction without altering the products of the reaction
- being itself unchanged chemically and in mass at the end of the reaction
Explain how the addition of a catalyst increases the rate of a
reaction in terms of activation energy
- catalysts decrease the activation energy by providing and alternative reaction pathway that has a lower activation energy
- as a result more of the particles have at least the minimum amount of energy needed for a reaction to occur when the particles collide
