Rates of reaction Flashcards
What is a chemical reaction
A change that involves rearranging atoms within reactant molecules and the formation of a new product. Evidence of a chemical reaction include colour change, temperature change, bubbles/fizzing, precipitate formation, odours and sounds
Rate of Reaction
The rate of reaction is the speed at which a reaction occurs. We can measure this by measuring:
The change in mass (if a gas is made)
the change in volume ( if a gas is made)
The change in colour or formation of a precipitate/ if the solution turns cloudy
Mean rate of reaction
= quantity of reactant used or product formed/time taken
Rate graphs
The rate of ant reaction does not stay the same. Firstly the rate of reaction is very fast as there are lots of reactant molecules available (concentration is high). Then it slows down as the reactant is being used up and the concentration of the reactant decreases. Lastly the reaction stops because the reactants have been used up.
Activation energy and collision theory
For a chemical reaction to happen, reactant particles must collide with each other and the particles must have enough energy for them to react. A collision that produces a reaction is known as a successful collision. Activation energy is the minimum amount of energy needed to start a reaction and if particles don’t have enough energy, they simply bounce off each other
Collision theory as an explanation of rate of reaction
Reactant particles are used up and the concentration of these particles decrease. This means that there are less frequent collisions/fewer collisions per second so the rate of reaction decreases/slows down.
Temperature
This increases the rate of reaction because particles gain more energy and so collide with each other more frequently with more speed so are more likely to exceed the activation energy and the rate of reaction increases.
Concentration
This increases the rate of reaction because there are more particles per unit of volume so collisions are more frequent which increases the rate of reaction. Concentration refers to aqueous solutions (liquid)
Catalysts
If you add a catalyst, the rate of reaction increases because a catalyst lowers the activation energy by providing an alternative reaction pathway. This raises the proportion of successful collisions
Surface area
This increases the rate of reaction because the surface are to volume ratio is bigger (particle size is smaller) . This would mean that the frequency of collisions would be higher making the rate of reaction higher. (Solid block<Small chunks<powder)
