HYDROCARBON COMPOUNDS

Hydrocarbons are the simplest organic compounds which contain only carbon and hydrogen. The other organic compounds consist of carbon, hydrogen, and other elements, for example glucose contains C, H, and O; protein contains C, H, O, N. A lot of organic compounds around us. The word Organic comes from Organism. So organic compound is a compound which concerns with organism. There are compounds which also contain carbon chain, but they aren't organic compounds. These compounds are classified as Carbon compounds; for example plastics, paper, and ruber. Wohler has found these group of compounds, started with ureum in his investigation.

The characteristics of carbon atom 

Atomic number of carbon atom is 6. Electronic configuration is 1s2 2s2 2p2. In the diamond, carbon atom bonds one of another through octet system, so that there are tetrahedral structure which link together. In organic compounds, carbon atoms form a chain. There are a variety of chains; they can be opened chain and closed chain. Hydrocarbon compounds which have an opened chain can be classified as alifatic hydrocarbons. Benzene is an aromatic hydrocarbon which is a special closed chain. The closed chain compounds are cyclic molecules. These compounds can be homocyclic and heterocyclic. The example of homocyclic is cyclo alkane. All the chains can be straight-chain and branched chain. 

Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions. 

CHANGING CONCENTRATION

In this reaction, all the substances are in the equilibrium. The proportion of the substances are constant, although there is still a forward reaction and reverse reaction. This microscopic change we couldn't see.
However, we can change this constant proportion by changing the concentration, for example by adding A, we increase the concentration of A. When [A]>, the collision between A and B caused the the rate of forward reaction > the rate of reverse reaction. The position of equilibrium lies to the right, because the equilibrium shifts to the right. When we increase [C], the equilibrium shifts to the left. When we decrease [D], the equilibrium shifts to the right.
According to the Le Chatelier Principle, when in the equilibrium we give an action, so the equilibrium will give back an action which named as a reaction to achieve the new equilibrium, so the process will be constant again.

ADDING CATALYST

Le Chatelier's Principle and catalysts

If you add a catalyst in the reversible reaction that in the equilibrium condition, so you do nothing. Its mean that the catalyst doesn't make any changing. Catalyst couldn' shift the position of equilibrium.
Do you remember what for the catalyst used as one of the factors affecting the reaction rate? The catalyst can speeds up the reaction, okay.
Now please think about the reversible reaction. There are two directions, the forward and reverse reactions. In the reversible reaction, if you add the catalyst before reaction, it will speed up the forward reaction and and immediately, the catalyst also speed up the reverse reaction till the rate reactions of both directions are the same, so there is a dynamic equilibrium. The dynamic equilibrium will be occured faster in the exist of catalyst. If you add catalyst in an equilibrium condition, it can affect the position of equilibrium.
A lot of dynamic equilibrium is very slow. This will cause of big problems in industrial processes. So the catalyst is still needed.

CHANGING TEMPERATURE

Using Le Chatelier's Principle with a change of temperature
Students, remember that in discussing the reaction rate, temperature is also one of the factors which affect the reaction rate.
If we think about changing temperature, so we have to look at the dynamic equilibrium, check the forward reaction, endotermic or exotermic.
If the forward reaction is endotermic, the sign of enthalpy change is positive. If the temperature is increased, what will happen? The endotermic reaction is a reaction which the reactants absorb the heat. So the kinetic energy of the reactants will increase and the number of efective collision will increase. Because of this, the reaction rate of the forward reaction is greater than the reverse reaction, so that the equilibrium will shift to the right and the concentration of products increase. The equilibrium constant is greater than the initial.
For another equilibrium, if the forward reaction is exothermic, the sign of enthalpy change is negative. The reverse reaction is endothermic and the sign of enthalpy is positive. If the temperature is increased, the products will absorb the energy and their kinetic energy will increase. The reaction rate of the reverse reaction is greater than the forward reaction. So the equilibrium will shift to the endotermic reaction, so it will shift to the left and the concentration of reactants increase; the equilibrium constant is smaller than before.
Why does the endothermic reaction absorb the energy when we increase the temperature?
According to Le Chatelier, the position of equilibrium will shift to counteract the change. This means that the position of equilibrium will shift so that the temperature is reduced again. (Action and reaction)
If the temperature of an equilibrium system is 200°C, and we increase the temperature to 300°C, what will happen? How can the reaction counteract the change we have made? What the reaction of this action? The reaction is there is a cooling down, to make the temperature reduces. The reactants will absorb the energy (heat) that we put in, so the equilibrium shift to the endothermic reaction.

CHANGING PRESSURE

Using Le Chatelier's Principle with a change of pressure

Lets discuss about changing pressure in reactions involving gases
What would happen if the condition of an equilibrium is changed by increasing the pressure?
According to Le Chatelier, the position of equilibrium will shift to a certain direction to counteract the change. That means that the position of equilibrium will shift so that the pressure is reduced again (If there is an action, there is a reaction).
The more molecules in the container, the higher the pressure will be. The system can reduce the pressure by reacting in such a way to produce fewer molecules.
For example : N2(g)+ 3H2(g) = 2NH3(g)
In this reaction, there are 4 molecules on the left-hand side of the equation, but only 2 on the right. By forming more NH3, the system causes the pressure to reduce.
Increasing the pressure on a gas reaction shifts the position of equilibrium towards the side with fewer molecules.
In summary, when P >, Volume <, equilibrium shift to the fewer molecules. N2 and H2 molecules are closely, the efective collision increases, the rate of forward reaction increases. The equilibrium will achieve after the rate of forward reaction = the rate of reverse reaction. The value of equilibrium constant is the same. What would happen if the condition of equilibrium is changed by decreasing the pressure? The equilibrium will shift to the left, because P <, Volume >, equilibrium will shift to the more molecules, e.i. N2 and H2 molecules.
Another example : H2(g) + I2(g) = 2HI(g).
In the above equilibrium, the number of molecules in the both sides are the same. What happens if P > ?
Increasing the pressure has no effect on the position of the equilibrium, because there are the same numbers of molecules on both sides.

LE CHATELIER'S PRINCIPLE

Now lets discuss about Le Chatelier's Principle. This scientist have investigated a dynamic equilibrium. He disturbed an equilibrium reaction by changing the condition of the reaction. When he changes the concentration of a reactant, from the color of the color of the substances he found that the color change. He disturbs both side, one by one, reactant and product.
From his finding, when a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.
Okay, now we use Le Chatelier's Principle with a change of concentration
For example an equilibrium reaction : A + B = C + D.
What would happen if you changed the conditions by increasing the concentration of A? According to Le Chatelier, the position of equilibrium will shifts to counteract the change. It means the position of equilibrium will shift, so the concentration of A decreases, because it reacts with B and it turns into C + D. The position of equilibrium shifts to the right. So if concentration of the left increases, the equilibrium shifts to the right. The Le Chatelier principle is very useful for industries, because this evidence can help them to determine which substance should be added to make the high profit. So they have to think an economical judgment. They have to find the cheapest raw materials rather than the expensive one.
Now, what would happen if you changed the conditions by decreasing the concentration of D (You remove the product from the equilibrium)?
The position of equilibrium will shift so that the concentration of D increases. It means that more A and B will react to replace the D that has been removed. The position of equilibrium shifts to the right. So if concentration of the right decreases, the equilibrium shift to the right.

DYNAMIC EQUILIBRIA

Reversible reaction is a reaction that can be occured in two directions, forward reaction and back (reverse) reaction. These reactions are happened at the same time.
Imagine a reaction : A(s) + B(aq) = C(aq) + D(g). This is in a closed system. We can think by using their color, for example B =blue and C = orange. At the same time blue --> orange and orange --> blue.
If the blue form turns into the orange one much faster than the the other one, so after the equilibrium can be achieved, the blue one becomes light and the orange one becomes dark. If this condition doesn't change again, the macroscopic change isn't happened but there is a dinamic change which is still occured constanously. This called a microscopic change and this reversible reaction named as a dynamic equilibrium.
Position of equilibrium
In the example above, the equilibrium mixture contained more orange than the blue ones. We can say :
"The position of equilibrium lies towards the orange."
"The position of equilibrium lies towards the right-hand side."
If the conditions of the experiment change (by adding reactant or product, so the macroscopic change will happen again), the composition of the equilibrium mixture will also change, till the equilibrium can be achieved.
Thinking about reaction rates
At the beginning of the reaction, the concentrations of A and B are at the maximum. The rate of the reaction is at its fastest.
As A and B react, their concentrations decrease, and the rate of the forward reaction falls as time goes on. At the same time, the concentration of C and D increases, and the rate of reverse reaction increases. At the equilibrium the rate of forward reaction= the rate of reverse reaction. (v1 = v2)

In summary, at equilibrium, the quantities of everything present in the mixture remain constant, although the reactions are still continuing. This is because the rates of the forward and the reverse reactions are equal.
If you change the conditions in a way which changes the relative rates of the forward and reverse reactions you will change the position of equilibrium or change the proportion of the subtances.
The charactheristic of dynamic equilibrium are :
1. Closed system
2. rate of forward reaction = rate of reverse reaction
3. Dynamic microscopic change
4. Constant proportion of substances

TYPES OF REACTION

There are two types of reaction, irreversible reaction and reversible reaction. The first reaction you have learnt till now. This reaction uses one arrow . This means that the reactants totally or completely react and form new substances.
This reaction is included neutralization, redox, decomposition, etc. In these reactions, all the reactants or one of the reactants are limited, after reaction no more reactants left or one of the reactant is nothing.
The second reaction uses two arrow; it means that the reaction can be occured in two directions, forward reaction and reverse reaction. This reaction can be occured in a closed system, so no substance will escape. If the reaction includes a gas, we have to close the equipment. If the reaction doesn' involve a gas, for example solid and liquid, so it doesn't need to close the equipment. The substances close theirselves. Because the closed system, so the reactants collide and form the products. At the same time the products collide and form the reactants again.
The example of both reactions are :
Zn(s) + HCl(aq) --> ZnCl2(aq) + H2(g) In the openned system.
N2(g) + 3 H2(g) = 2 NH3(g) In the closed system.

THE EFFECT OF CATALYSTS ON REACTION RATES

Another factor that affects reaction rates named catalyst.
A catalyst is a substance which can speeds up a reaction, but is unchanged at the end of the reaction. The catalyst reacts in the intermediate process.
When certain reactants mix, the reaction is very slow. The possible reason is the activation energy is very high. The molecular energy is not enough. Last discussion, you heat the reactants to increase the molecular energy till the same as the activation energy. The work of catalyst differs. The catalyst will combine with one of the reactant and immediately the other reactant combine with the first. At that time, catalyst is separated and appeared again. This catalyst is exactly the same as before. The energy used to combine the reactants is the same as the molecular energy. This named as new activation energy. So this energy is lower than the original activation energy used in the reaction without catalyst.

THE BEST COLLISION FOR REACTION

When reactants start to react, they must have an enough energy for collision. This energy is named Activation Energy. This is a minimum amount of the energy required for best collision. Because of this energy, the bond between particles will break and each atoms will separate one of another. However, there is an important factor which should be taken into account, that is the right position of collision. Although the energy required is enough, if the collision is not in the right position, so reaction isn't occurred.
In conclusion, there are two important points for a collision to make reactants can start reaction. Please use this collision theory to explain factors that affect reaction rates.

THE EFFECT OF PRESSURE ON REACTION RATES

This moment we will discuss the change of pressure on reaction rates. The change of pressure only affects the rate of reaction involving gas. If the reaction involves solids or liquids, the change of pressure has no effect on the rate. Why thats difference? Think about the difference of the position of their particles.
What happens if you increase the pressure on a reaction involving gases?


Look at this equation. When you change the pressure, the number of molecules in certain volume also changes.

NAMING COVALENT COMPOUNDS

Binary Compounds of Two Nonmetals
Given Formula, Write the Name
We will discuss how to name binary compounds from the formula when two nonmetals are involved.
In this compound, you do not even need to know the charges, because it is a covalent compound, no metal here. Use Greek number for prefix. Here are the first ten:
one mono- six hexa-
two di- seven hepta-
three tri- eight octa-
four tetra- nine nona-
five penta- ten decen a-
1. N2O Dinitrogen oxide
2. Cl2O7 Dichlor heptoxide
Given Name, Write the Formula
1. Nitrogen dioxide, NO2
2. Carbon tetrachloride, CCl4

NAMING IONIC COMPOUNDS

In naming ionic compounds, there are some rules. The first rule is proposed for ionic compounds which have a single cation and a single anion, so this compound consists of 2 different elements, metal and non metal. This compound can be grouped as a binary ionic compound. There is a different binary compound, i.e. a covalent compound.
Binary Compounds of Cations with a single charge.
Given Formula, Write the Name
In your textbook there is a table contains list of cations and anions.
1. Na+ and Cl- forms NaCl, sodium chloride
2. Na+ and O2- forms Na2O, sodium oxide
3. Al3+ and F- forms AlF3, aluminium fluoride
Please remember that all elements involved in the compounds have ONLY ONE charge. It includes both the cation and the anion involved in the formula.
The order for naming a binary compound is first the cation, then the anion.
Use the name of cation with a fixed charge directly from the periodic table.
The name of the anion will be made from the root of the element's name plus the suffix "-ide."
Given Name, Write the Formula
The order for writing a formula is first the cation, then the anion.
You have to know the charges of each cation and anion.
The sum of the positive charge and the sum of the negative charges must add up to zero, because compound is neutral.
You may adjust the subscripts to get a total charge of zero. Don't change the charge of each ion.
1. Potassium sulfide, K2S
2. Barium bromide, BaBr2
Binary Compounds of Cations with Variable Charges
Given Formula, Write the Name
The cations involved at least have 2 charges. In your texbook there is a list of cations with variable charges. For example : Cu +1 and +2; Fe +2 and +3; Hg +1 and +2; Pb +2 and +4; Sn +2 and +4; Au +1 and +3.
1. FeCl2, Iron(II) chloride
2. Cu2O, Copper(I) oxide
Polyatomic Compounds
There are polyatomic cations and anions. This compound consists of monoatomic cation and polyatomic anion or polyatomic cation and monoatomic anion or both cation and anion are polyatomic.
1. K2SO4, Potassium sulphate
2. (NH4)2S, Ammonium sulfide
3. NH4NO2 Ammonium nitrite

BOND ENERGY

Bond energies (BE) are defined as the energies required to break the chemical bonds of substances. So this is an endotermic process, the value is positive. In calculating the enthalpy change of a reaction, you can use the following formula :
DHreaction = SUM (BEreactants) - SUM (BEproducts)
Now do the following exercise :
The bond energy (kJ/mol) for H2, F2, and HF are 436, 158 and 568 kJ/mol respectively. Calculate the enthalpy change of : H2(g) + F2(g) --> 2 HF
Since bond energies are given, use the monoatomic gases.
After calculating the enthalpy change, draw a diagram.

STANDARD ENTHALPIES FORMATION

Using Formulas to Calculate enthalpy change.
The enthalpy change of a reaction can be calculated through the use of formulas. This formula depends on whether enthalpies of formation or bond energies are available.
When standard enthalpies of formation, DHfo, for all products and reactants are available, you have to use the following formula :
DHreaction = SUM (DHproducts) - SUM (DHreactants)
For simplicity in formulation, use DH to represent DHfo in the above formulas. D is delta, DH is enthalpy change, f is formation, and o is standard.
Calculate the enthalpy change of the following reactions by using a table of DHfo.
1. Calculate the enthalpy change of burning methane gas.
2. Calculate the combustion enthalpy of propane gas and butane gas.

HESS' LAW

This is Germain Henry Hess. In the study of thermochemistry, there is an important law from him named 'HESS' LAW'. This is a principle of conservation of energy.

Hess' Law states that the heat evolved or absorbed in a chemical reaction is the same whether the reaction takes place in one or in several steps. This is also known as the law of constant heat summation.

Hess's law is important because it provides a practical way to combine thermochemical equations for known 'step' reactions to get a thermochemical equation for some 'target' reaction. The basic procedure is :
1. Write all the thermochemical equations for the step reactions.
2. Write the balanced chemical equation for the target reaction.
3. Reverse step reactions so products/reactants match the target reaction.
4. Scale step reactions so products/reactants that don't appear in the target reaction will cancel out.
5. Add the step reactions.
6. Scale the resulting reaction so it matches the target reaction

Okay students, you have to apply this law. Please find an exercise from your textbook and try to do summation of step reactions to find the enthalpy change of the target reaction. Firstly, do the simple equation, focus on 2 step reactions.

DIPOLE INDUCED DIPOLE FORCES

Remember about the force between non-polar molecules, for example argon. The element of argon consists of atom, we call as a monoatomic molecule. In argon atom, there is also an intermolecular force, but this force is really very weak because this atom has no dipole moment. The temporary dipoles are only occurred very rare compare with diatomic molecules, as happened in iodine, I2 molecules.

Now, what would happen if we mixed HCl with argon? The electrons on an argon atom are distributed homogeneously around the nucleus of the atom. When an argon atom comes close to a polar HCl molecule, the electrons can shift to one side of the nucleus to produce a very small dipole moment that occurredin a fraction of time. This is very weak temporary dipoles.
According to this evidence, by distorting the distribution of electrons around the argon atom, the polar HCl molecule induces a small dipole moment on this atom, which creates a weak dipole-induced dipole force of attraction between the HCl molecule and the Ar atom.

DIPOLE FORCES

Now lets discuss about dipole forces. The example of this force is HCl as a polar molecule. Polar molecules are sometimes described as "permanent dipoles" or "dipoles". Each molecule has two "poles" permanently. One end (pole) of the molecule has a partial positive charge while the other end has a partial negative charge. The molecules will orientate themselves so that the opposite charges attract effectively.
In the example on the left, hydrogen chloride is a polar molecule with the partial positive charge on the hydrogen and the partial negative charge on the chlorine. A network of partial + and - charges attract molecules one of another.

IONIC FORCES

The physical properties of melting point and boiling point, for example, are related to the strength of attractive forces between molecules. These attractive forces are called Intermolecular Forces.
In an ionic bonding, there is an ionic force. This force is commonly called electrostatic force (Coulomb).
Each Na+ ion and Cl- ion attracts one of another, so that they forms a Crystal.
Although there is a repulsion between inner electrons of Na+ and outer electrons of Cl-, the ionic force is much stronger than the repulsion.
The ionic force is much stronger than the molecular force, so boiling point and melting point of ionic compounds are higher than covalent compounds. The last force will be discussed later.

INDUCED DIPOLE FORCES

Now lets think about intermolecular forces. There are three different forces, force between non-polar molecules, non-polar and polar molecules, and polar molecules.
Forces between non-polar molecules are the weakest of all intermolecular forces.
In the non-polar molecules there are 'Temporary dipoles" which are formed by the shifting of electron clouds within molecules. These temporary dipoles attract or repel the electron clouds of non-polar molecules.
The temporary dipoles exist for a fraction of a second, so a force of attraction exist for that fraction of time. The strength of induced dipole forces depends on how easily electron clouds can be distorted. Atoms or molecules which have many electrons are more easily distorted, because these electrons are far from their nucleus.
Okay, please explain about intermolecular forces in iodine molecules as shown in the picture. Give the reason why in the iodine molecule, atom that has the negative temporary pole is bigger than atom with positive temporary pole,