Rates of Reactions Flashcards
What is the Rate of a Reaction
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
Does increasing concentration decrease or increase the rate of a reaction?
Increasing concentration, increases the rate of a reaction.
At lower concentration the reaction time is _____.
longer
At high concentrations the reaction time is _______.
shorter
What is a catalyst?
A catalyst is a substance that alters the rate of a chemical reaction but is not consumed in the reaction.
What does hydrogen peroxide decompose into at room temperature and what happens if you add manganese dioxide?
Hydrogen peroxide decomposes into water and oxygen at room temperature, the addition of manganese dioxide as a catalyst causes hydrogen peroxide to decompose faster.
What are the properties of catalysts?
Remain chemically unchanged at end of reaction.
Specific - work for one reaction but not another.
Only needed in small amounts.
In equilibrium reactions, a catalyst helps equilibrium to be achieved quicker.
What are the 3 types of catalysis?
- Homogenous 2. Heterogeneous 3. Autocatalysis
What is homogenous catalysis?
Both reactants and catalyst are in the same phase (same physical state). There is not boundary between the reactants and the catalyst.
Give an example of homogenous catalysis.
E.g. Both reactants and catalyst are liquids - aqueous potassium iodide and hydrogen peroxide, potassium iodide breaks H2O2 into water and oxygen
What is heterogeneous catalysis?
Reactants and catalyst are in different physical states. There is a boundary between the reactants and the catalyst.
Give an example of heterogeneous catalysis.
E.g. Hydrogen peroxide (liquid) and manganese dioxide (solid) or oxidation of methanol by platinum catalyst.
What is autocatalyis?
Autocatalysis is where one of the products of a reaction catalyses the reaction.
Give an example of autocatalysis.
E.g. Reduction of Manganate (VII)
MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O
-Mn2+ catalyses the reaction
-Purple colour decolorises slowly
-Then decolorising speeds up due to Mn2+ ions produced, catalysing the reaction.
What is chemical equilibrium?
Chemical Equilibrium is a state of dynamic balance where the rate of the forward reaction equals the rate of the reverse reaction.
