C6: Rates Of Reaction Flashcards
What is the rate of reaction?
The rate of a chemical reaction is how fast the reactants are changed into the products.
Give a few examples of slow reactions.
The slowest is the rusting if metal.
Other slow reactions include chemical weathering - like acid rain damage to limestone buildings.
What is an example of a moderate speed reaction?
The metal magnesium reacting with an acid to produce a gentle stream of bubbles.
Give an example of fast reactions.
Burning is a fast reaction, but explosions are even faster and release a lot of had. Explosive reactions are all over in a fraction of a second.
How can you find the speed of reactions?
By recording the amount of product formed, or the amount of reactant used up over time.
What shape does a fast reaction take on a graph?
The steeper the line in the graphic the faster the rate of reaction.
Over time the line becomes less steep as the reactants are used up.
The quickest reactions have the steepest lines and become flat in the least time.
What are the requirements for a reaction to take place?
For a reaction to take place, two reactants must collide - if the collision results in a reaction it is a fruitful collision.
The particles must also have enough activation energy in order to react together.
How do catalysts speed up reactions?
Different catalysts are needed for different reactions, but they all work by decreasing the activations energy needed for the reaction to occur. They do this by providing an alternative pathway with a lower activation energy.
What is the equation for average rate of reaction?
Amount of reactant used/Amount of product formed over the Time
What are the units?
Volume change: cm3s-1
Reactant mass: gs-1
How are reaction rates explained by collision theory?
The rate of a chemical reaction depends on:
1) The collision frequency of reacting particles (how often they collide). The more collisions there are the faster the reaction.
2) the energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful.
What four things does the rate of reaction depend on?
Temperature
Concentration or pressure
Surface area
Presence of a catalyst
All four factors that can increase the rate can be explained in terms of increasing the number of successful collisions.
How does increasing the temperature increase the rate?
1) When the temperature is increased, all the particles move faster.
2) This causes them to collide more frequently.
3) And the faster they move the more energy they have, so more collisions will be successful.
How does increasing the concentration increase the rate?
If a solution is more concentrated, there are more particles in the same volume.
Similarly, when the pressure of gas is increased, there are the same number of particles occupying a smaller space.
This makes collisions more frequent.
How does increasing the surface area speed up the rate?
If one of the reactants is solid, breaking it into smaller pieces will increase its surface area to volume ratio.
So for the same volume of the solid, the particles around it will have more area to work on - so the collisions will occur more frequently.
