Chapter 1: Rate of Reaction
Definition
Speed at which reactants are converted into products in a chemical reaction.
Thus, the reactants is quickly converted to the products.
Thus, the rate of reaction is high/higher.
Slow reaction;- time taken is long
Thus, the reactants is slowly converted to the products.
Thus, the rate of reaction is low/lower.
Hence;
What is the relation between rates of reaction with time?
When the time taken is longer, the rate of reaction is lower,
Rate of reaction is directly proportional with 1/time
Rate of reaction is inversely proportional with time
Measuring the rate of reaction
Suitable changes;
volume of gas liberated
precipitate formation
change in mass during the reaction
colour changes
temperature changes
pressure changes
Other observable changes?
Average rate of reaction :
The average value of the rate of reaction within a specified period of time.
Notes:
Reaction with high rate of reaction, completed in short time.
Reaction with low rate of reaction, completed in longer time.
Rate of reaction at given/Instantaneous time :
The actual rate of reaction at that instant (Gradient of the curve at that instant)
Collision Theory
Dear boys and girls to better understand of collision theory you must know few thing
related to the theory which is;
Collision
Effective collision
Activation energy
Collision frequency
Effective collision frequency
Energy profile diagram
* And also the chemical equation
What is the Collision Theory?
During a reaction, the particles of the reactants must collide with each other for bond breaking
and then bond formation product. to occur to produce
Bond breaking : absorb heat energy
Bond formation : release heat energy
Those collisions which achieved a minimum activation energy and with the correct orientation will result in a reaction. These collisions are called effective collisions.
If the particles collide with less energy than activation energy or with wrong orientation,
it will not result in reaction, is called ineffective collisions.
Effective collisions
Those collisions which achieved a minimum activation energy
and with the correct orientation, will result in a reaction.
Activation energy
Activation energy is the energy barrier that must be overcome by the colliding particles of the reactants in order for reaction to occur
Activation energy is the difference in energy between the energy in reactants and the energy at the peak of curve
Energy Profile Diagrams for Exothermic Reaction
[click here to see the diagram]|
| Reactants | Product |
| Total Heat Energy | Higher | Lower |
| Heat Energy during reaction | Energy absorbs during bond breaking is lower | Energy releases during bond formation is higher |
Thus;
Heat changes = Heat Energy in product – Heat Energy in reactant
= - ve
Energy Profile Diagrams for Endothermic Reaction
[click here to see the diagram]|
| Reactants | Product |
| Total Heat Energy | Lower | Higher |
| Heat Energy during reaction | Energy absorbs during bond breaking is higher | Energy releases during bond formation is lower |
Thus;
Heat changes = Heat Energy in product – Heat Energy in reactant
= + ve
Factors Affecting The Rate of Reaction
1) Total surface area of solid reactant
2) Concentration of reactant
3) Temperature of reactant
4) Use of catalyst
5) Pressure of gaseous reactant
Effect of Size
When the size of fixed mass of solid reactant is smaller,
The total surface area per volume exposed to collision with other reactant particles is
bigger.
Thus, the number of collision among the reacting particles reactants increases.
Thus the Frequency of collisions is higher.
Thus, the number of collision achieved the activation energy to become effective collision is
also increases.
Thus the frequency of effective collisions is higher.
Hence, when the size of fixed mass of solid reactant is smaller, the rate of reactions is higher.
Effect of Concentration
When the concentration of the solution of a reactant increases;
The number of particles per unit volume of the solution of the reactant also increases.
Thus, the number of collision among the reacting particles reactants increases.
Thus the Frequency of collisions is higher.
Thus, the number of collision achieved the activation energy to become effective collision is
also increases.
Thus the frequency of effective collisions is higher.
Hence, when the concentration of the solution/reactant is higher, the rate of reactions is higher.
Effect of Temperature
When the temperature of a reactant increases;
The kinetic energy of reacting particles will increase, so the particles moves faster.
Thus, the number of collision among the reacting particles reactants increases.
Thus, the Frequency of collisions is higher.
Thus, the number of collision achieved the activation energy to become effective collision is
also increases.
Thus, the frequency of effective collisions is higher.
Hence, when the temperature of the reactant is higher, the rate of reactions is higher.
Effect of Catalyst
Catalyst is a substance which alters the rate of chemical reaction while it remains
chemically unchanged at the end of the reaction.
Activation Energy profile diagram
When the catalyst is presence;
The catalyst allows the reaction to take place through an alternative path which requires
a lower activation energy.
Thus, more collision among the reacting particles are able to achieve the lower activation energy.
Thus, the number of collision achieved the activation energy to become effective collision is
also increases.
Thus, the frequency of effective collisions is higher.
Hence, when the catalyst presence, the rate of reactions is higher.
Effect of Pressure
When the pressure of the gas of a reactant increases;
The number of particles per unit volume of the gas of the reactant also increases.
Thus, the number of collision among the reacting particles reactants increases.
Thus, the Frequency of collisions is higher.
Thus, the number of collision achieved the activation energy to become effective collision is
also increases.
Thus, the frequency of effective collisions is higher.
Hence, when the temperature of the reactant is higher, the rate of reactions is higher.
The End
Chapter 2: Carbon Compound
Alkanes
1. General Formula : CnH2n+2 (number of atoms, n = 1,2,3......)
2. They are saturated hydrocarbons;
each carbon atom is bonded to four other atoms by
single covalent bonds.
3. The members of the family, ending with name “ane”.
Physical Properties
Physical properties of alkanes
i. cannot conduct electrity
ii. less dense than water
iii. obeys “ like dissolve like”;
· dissolve in organic solvents
· insoluble in water
iv. low melting and boiling points
Conclusion:
- molecule held together by weak intermolecular forces
- properties of covalent compound
- gradually steady increase as the number of carbon in alkane
increases
Chemical Properties
Reactivity of alkanes
1. Not reactive/unreactive because saturated hydrocarbon
2. Did not decolourized purple solution of acidified potassium manganate(VII)
3. Did not decolourized reddish brown solution of bromin water
4. Neutral.
Combustion of alkanes
1. In the presence of sufficient oxygen, alkanes burns to form carbon dioxide and water.
Chemical equation:
i. CH4 + 2O2 → CO2 + 2H2O
ii. C2H6 + 7 O2 → 2CO2 + 3H2O
2
2C2H6 + 7 O2 → 4CO2 + 6H2O
iii. C4H10 + 13/2 O2 → 4CO2 + 5H2O
iv. C6H14 + 19/2 O2 → 6CO2 + 7H2O
Alkenes [click here to see the notes]
Alcohol [click here to see the notes]
Carboxilic Acids and Ester [click here to see the notes]
Fats [click here to see the notes]
Rubber [click here to see the notes]
Simple Countdown
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