Rates of reactions and Particle Theory Flashcards
What is the particle theory?
The particle theory states that all matter is made up of tiny particles (atoms, ions or molecules) and that these particles are in constant motion.
-Temperature affects the speed of particles
What is the collision theory?
The collision theory states that in order for a chemical reaction to occur, two or more REACTANT particles must collide with sufficient force (activation energy - minimum amount of energy required for a chemical reaction to proceed) and with the right orientation.
Why is activation energy needed for chemical reactions?
Because bonds need to be broken and new bonds need to be formed.
So Ea is the energy needed to break bonds and form new bonds
What are the 4 factors which affect rate of reaction?
- Temperature
- Concentration
- Surface area
- Catalysts
How does temperature affect the rate of reaction?
As temperature increases, the rate of reaction increases.
This is because the higher temperature means the reactant particles move MORE QUICKLY because they have more KINETIC energy as temperature is the measure of the average kinetic energy of the particles. This also means that there is a greater chance of the collision resulting in a reaction (ie have enough energy to overcome the activation energy barrier). More energetic particles have a higher chance of COLLIDING SUCCESSFULLY because they will collide more often thus increasing the number of successful collisions PER SECOND, thus increasing the rate of reaction.
How does concentration affect the rate of reaction?
As concentration of a reactant/s increases, the rate of reaction increases.
This is because there are more reactant particles PER ML meaning that reactant particles are more numerous and closer together, so the frequency of collisions increase and the frequency of successful collisions increase as more collisions are effective, resulting in the increased rate of reaction.
How does surface area affect the rate of reaction?
As surface area of a reactant/s increases, the rate of reaction increases.
This is because more particles are exposed, increasing the surface area available for collisions to take place, allowing more particles to collide.
-has NO effect on the energy of the particles.
Stirring to dissolve a solute in a solvent increases the surface area of the solute exposed to the solvent, thus increasing the frequency of collisions and therefore the rate of successful collisions
Total number of collisions do not change assuming that the amount of reactants remains constant so faster rate of reaction
How do catalysts affect the rate of reaction?
Catalysts are special chemicals that speed up the rate of reaction but do not get used up themselves. Catalysts work by providing an alternative pathway that has a lower activation energy required than normal, meaning that more reactant particles collide with sufficient energy to enable successful collision. ie effectiveness of the collisions has increased.
How are rates of reaction measured?
- Measure how quickly the products are made
- measure how quickly one of the reactants disappears
- pH change
- how quickly colour changes
Observing rate of reaction on graph
- Steeper line when reaction starts because fastest reaction rate due to highest concentration of reactants.
- Horizontal = reaction stopped
- The amount of reactants decrease rapidly at the start, and flattens out as they are used up.
Metal and acid reaction
Sandpaper off the metal oxide coating otherwise reaction would not occur or would slow down rate of reaction.
