What is the rate of a chemical reaction determined by?
Rate of reaction = change in concentration/ time for change to happen
How is rate of reaction measured?
Need to find out how fast one of the reactants is being used up
How fast one of the products is being formed
How can the rate of reaction be determined in a concentration against time graph?
The gradient of the graph indicates the rate of reaction.
The gradient decreases as the rate increases and becomes 0 when the reactant is used up
Gradient = y/x
y= change in concentration x = change in time
What is collision theory?
A + B > C + D
in order for molecule A to react with molecule B the 2 molecules must collide with each other and they may react.
Not all collisions between molecules result in a reaction.
What are the requirements for reactions to occur?
The 2 molecules must collide with sufficient energy to cause a reaction (AE)
The 2 molecules must collide in the correct orientation
What is Activation energy?
If the particles collide with less energy than the Activation energy, they simply bounce apart and no reaction will occur. Activation energy is the barrier to the reaction. Only those collisions that have energies equal to or greater than AE result in reaction.
Chemical reactions result in the breaking of some bonds and making of new ones. Some bonds have to be broken before new ones can be made AE is involved in the breaking of some original bonds.
Where collisions and relatively gentle there is not enough energy available to start the bond-breaking process so particles do not react.
What is Orientation?
between ethene and hydrogen bromide the reaction can only happen if the hydrogen at the end of the H-Br molecule approaches the C=C on ethene. Any other collisions between the 2 molecules result in the molecules bouncing of each other.
What is Steric hindrance?
When the shapes of molecules influence reactions say there is steric factor involved in the reaction. Some cases atoms in a molecule can hinder the course of a reaction if they are large they can get in the way of attacking species in this case steric hindrance.
How can a reaction be sped up?
To increase the rate of reaction need to increase the frequency of collisions with sufficient energy between the reactant particles successful collisions
What is the effect of concentration of rate of reaction?
For reactions in a solution an increase in concentration causes an increase in reaction rate. if the concentration of a solution is increased then the frequency of collisions between the reacting solute particles increases. More in a given volume frequency of successful collisions increases increasing rate of reaction.
What is the effect of pressure on rate of reaction?
For reaction which molecules collide and react in gas phase an increase in pressure will increase the rate of reaction.
If pressure of the gaseous mixture is increased increase in reactant molecules in a given volume. So frequency of collisions will increase increasing the rate of reaction.
Changing pressure has no effect on reaction in the solid or liquid phase.
What is the effect of surface area on rate of reaction?
For heterogeneous reactions involving a solid with a large surface area will result in faster rate of reaction
Mg + 2H+ > Mg2+ + H2
in this reaction collisions will occur on the surface of the magnesium higher rate of reaction if the Mg is powdered the surface area increases and the H2 gas is given off more quickly
What is the Maxwell-Boltzmann distribution curve?
The molecules in a sample of a gas have a wide range of energies. in order to estimate what fraction of collisions will have the required AE need to know the energy distribution of the molecules.
T1 is a lower temperature than T2
What are the important points about this curve?
Neither curves are symmetrical.
Both curves start at the origin and finish approaching the x-axis asymptotically.
The area under each curve is the same since the number of molecules has not changed.
The peak of T2 is displaced to the right and is lower than that for the peak of T1.
What does the shaded area show?
Represents the fraction of molecules that have the required energy to react at T1.
The combined area shaded in dark green represents the fraction of molecules that has the required energy to react at T2
Fraction of molecules that react at higher temperature is greater.
How can changes in temperature affect the rate of reaction?
An increase in the temperature increases the fraction of molecules that possess the required AE. The rate of reaction increases because the number of successful collisions per second increases.
How do particles collide in solution?
In the gas phase molecules are moving around at high speeds and so frequently collide with one another.
In solution molecules are more closely packed together so a lot of space between them. In low-to-medium concentrations most of the solutions is solvent, so solute particles are entirely surrounded by them. Trapped in a solvent cage.
There is situations in which a number of solute molecules become trapped in the same solvent cage. This increase the collisions rate between the solute particles and if enough energy may react.
What are the stages of a reaction in a solution?
All the molecules have to come together by a process of diffusion into the same solvent cage.
Then they have to react
May be some reactions in which molecules encounter one another.
What is the effect of a catalyst on the rate of reaction?
A catalyst provides an alternative route for the reaction with lower AE than the other route.
The blue shaded area represents the fractions of molecules that have E>EA when no catalyst
The combined green and yellow show fraction of molecules with greater energy when catalyst is present.
What are reaction profile diagrams?
Reaction profile is extension of enthalpy change diagram it shows the enthalpy levels of the reactants and products includes EA for the reaction.
What does a reaction profile look like for a catalysed reaction
How are catalysts used in industry?
Catalyst increase the rate of a chemical reaction meaning more of the desired product can be made in a given time
Reactions can take place at a lower temperature decreasing the energy cost to manufacture.
Most catalysts in industry are heterogeneous catalysts one that has different phase to that of the reactant. Solids are used for reactions involving gases. Iron in the Haber process.
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Solubility rules3
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General eqautions10
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Common ions29
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1 - Atomic structure and periodic table47
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2.1.1 [Metallic bonding]6
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2.1.2 [Ionic bonding]11
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2.1.3 [Covalent bonding]7
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2.1.4 [Electronegativity and bond polarity]11
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2.2.1 [Bonding in discrete molecules]4
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2.2.2 [Dative covalent bonds]3
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2.2.3 [Shapes of molecules]13
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2.2.4 [Non polar and polar molecules]9
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2.2.5 [Intermolecular interactions]9
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2.2.6 [Intermolecular Interactions and physical properties13
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2.3.1 [Solid lattices]13
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2.3.2 [Structure and properties]6
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3.1 - Electron loss and gain7
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3.2 [Oxidising and reducing agent]7
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4.1 [Group 2]41
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4.2 [Group 7]36
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5.1 [Empirical, Molecular Formula and Ideal gas equation]12
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5.2 [Calculations using moles and the Avogadro's constant]14
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5.3 [Concentrations of solutions, Preparing a standard solution and titration]31
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5.4 [Mistakes, errors, Accuracy and precision. Measurement uncertainty Percentage measurement uncertainty]10
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5.5 [ Yield of reaction. Atom economy]7
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6.1 [Introduction to organic chemistry]26
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6.2 [Hydrocarbons]66
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6.3 [Halogenalkanes]21
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6.4 [Alcohols]30
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7 [Modern analytical techniques]18
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8.1 [Heat energy and enthalpy]28
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8.2 [Bond enthalpy]4
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9 [Kinetics]22
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10 [Equilibrium]25
