Rates of reaction Flashcards
What is the rate of a chemical reaction?
- how fast the reactants are changed into products
What is an example of a moderate speed reaction?
- metal magnesium reacting with an acid to produce a gentle stream of bubbles
What does the rate if a chemical reaction depend on?
1- collision frequency of reacting particles
- the more collisions there are the faster the reaction is
2- energy transferred during a collision
- particles have to collide with enough energy for the collision to be successful
What is activation energy?
- minimum amount of energy that particles need
Why do particles need activation energy?
- particles need this much energy to break the bonds in the reactants and start the reaction
What is the four things that affect rate of reaction?
- temperature
- concentration of a solution or the pressure of a gas
- surface area
- catalyst
How does increasing temperature increase rate of reaction?
- when temperature is increased particles move faster
- so they have more collisions
-higher temperature increases energy of the collisions because the particles are moving faster - reactions only happen if the particles collide with enough energy
- so at higher temperatures there will be more successful collisions
- so increasing temp increases rate of reaction
How does increasing concentration (or pressure) in a solution increase rate of reaction?
- if a solution is made more concentrated it means there are more particles of reactant in the same volume
- this makes collisions more likely
- so reaction rate increases
How does increasing concentration (or pressure) in a gas increase rate of reaction?
- increasing pressure means that the particles are more crowded
- the frequency of the collisions between particles will increase
- so rate of reaction will also increase
How does surface area (smaller solid particles) affect rate of reaction?
- breaking a solid into smaller pieces will increase surface area to volume ratio
- more solid exposed
- particles around it will have more area to work on
- so frequency of collisions will increase
- rate of reaction is faster for solids with a larger surface area to volume ratio
What is a catalyst?
- substance which increases rate of reaction without being chemically changed or used up in the reaction
How do catalysts work?
- decreases activation energy needed for a reaction to occur
- they do this by providing an alternate reaction pathway that has lower activation energy
How can you calculate rate of reaction?
rate of reaction= amount of reactant used or amount of product formed/time
How can you do a precipitation reaction to find rate of reaction?
- mix two see through solutions
- producing a precipitate which clouds the solution
- mix the two reactant solutions and put the flask on a piece of paper that has a mark on it
- observe the mark through the mixture and measure how long it takes for the mark to be obscured
- the faster it disappears the faster the rate of reaction
How can you find the rate of reaction with the change in mass experiment?
- as the gas is released the lost mass is easily measured on the balance
- the quicker the reading on the balance drops, the faster the rate of reaction
- you know the reaction has finished when the reading on the balance stops changing
- do experiment in fume cupboard
How can you find the rate of reaction with the volume of gas given off experiment?
- involves using a gas syringe to measure volume of gas given off
- more gas given off during a set time interval, the faster the rate of reaction
- you can tell when the reaction is finished when no more gas is produced
- plot a graph of gas volume against time elapsed
How can you measure how surface area affects rate of reaction?
- measure volume of gas produced using a gas syringe
- take readings at regular time intervals
- repeat experiment with the same volume/concentration of acid and the same mass of marble chips, but with the marble chips more crunched up
- repeat with the same mass of powdered chalk
What is a experiment to show how reaction rate is affected by temperature?
- sodium thiosulfate and hydrochloric acid are both clear solutions
- but they react together to form a yellow precipitate of sulfur
- measure rate by watching a black mark disappear through cloudy sulfur and timing how long it takes to go
- reaction can be repeated for solutions at different temperatures
- the best way is to use a water bath to heat both solutions to the right temp before you mix them
What does the temperature rate of reaction show?
- higher the temp the quicker the reaction
- therefore, the less time it takes for the mark to disappear
What is the decomposition of hydrogen peroxide?
- 2H20 = 2H20 + 02
What are some examples of catalysts that can be used?
- manganese oxide, copper (ii) oxide, zinc oxide
What is the method with a catalyst?
- add some mno2 powder to the h2o2
- measure volume of gas produced at regular time intervals
- record results
- repeat experiment with exactly the same volume/concentration of hydrogen peroxide but using a different catalyst
