Rates of Reactions
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What are Rates of Reactions?
The rate of reaction is the change in concentration per unit time of any one reactant or product
What are factors affecting rate of reaction?
Nature of reactants, particle size, concentration, temperature, catalysts
How do you draw rate graphs?
Concentration v. (1/Time) or Temp v. (1/Time) (1/Time) used as Rate and Time inversely related (shorter time means faster rate) Be careful with units of 1/time
Catalyst
is a substance that alters the rate of reaction but is not consumed in the reaction
Homogeneous catalysis
Homogeneous catalysis occurs when the reactants and the catalyst are in the same phase. example =?
Heterogeneous catalysis
Heterogeneous catalysis occurs when the reactants and the catalyst are in different phases
Autocatalysis
Occurs when on of the products of the reaction catalyses the reaction. e.g. Mn2+ ions in KMnO4 titrations (purple changes to colourless more quickly as titration proceeds
Mechanisms of Catalysis
Intermediate Formation theory Surface Adsorption theory
Collision Theory
For a reaction to occur the reacting particles must collide with each other. A collision only results in a product being formed if a certain minimum energy is exceeded (called activation energy)
Activation Energy
The minimum energy which colliding particles must have for a reaction to occur
How to calculate instantaneous rate?
• Draw a tangent to the curve • Draw a right angle with the tangent as the hypotenuse. • Slope = tan Theta = DeltaV over Delta T
Draw how to calculate instantaneous rate and explain each part.
.
What conditions need to be in place for a reaction to occur?
Particles must collide if a reaction is to take place. They must do so with sufficient energy. They must collide effectively and frequently.
Factors that effect the rate of a reaction
Concentration, Catalyst, Area, Temperature and Nature of reactants.
What are the nature of reactants of covalent compounds?
Slow Reactions Bonds are broken before new ones are formed
What are the nature of reactants of Ionic compounds?
Fast Reactions Oppositely charged ions come together
How does temperature affect rates of reaction?
Hotter the temperature - the more energy the particles have - the faster the particles move. Therefore, more effective and frequent collisions and the reaction occurs quicker. Therefore, the higher the temperature, the shorter the reaction time.
At lower temperatures, the reaction time is ______.
longer
At higher temperatures, the reaction time is _______.
shorter
Draw an example graph of a reaction with time on the y axis and temp. on the x axis.
.
Does increasing concentration decrease or increase the rate of a reaction?
Increasing concentration, increases the rate of a reaction.
For H2O2, what does increasing concentration do and why?
For H2O2 - increasing concentration, increases the amount of product (gas) produced, as it is the only reactant present
What does increasing concentration cause for hydrochloric acid and sodium thiosulphate?
For hydrochloric acid and sodium thiosulphate - increasing concentration causes the same amount of gas to produced but in a shorter time.
At lower concentration the reaction time is _____.
longer