Sodium hydroxide

Sodium hydroxide is probably the best known STRONG ALKALI. It is pH 11. If you see it as one of the products in a reaction, you will know that the solution has become alkali.
If you think about it, the pH has gone UP. pH11 is UP from pH7. The pH goes DOWN to make acids.

Intermolecular forces

Water has a low boiling point because the forces between the molecules are weak. On the diagram, the forces between H and O are strong covalent bonds. It takes a lot of energy to break up water into H and O. However, it is easy to separate the molecules. In an exam answer, you need to make it clear that it is the inter-molecular forces that you are talking about.

Metallic bonding

Metals have big atoms and so the force of attraction between the nucleus and the outer electrons is weaker. The electrons can wander off. Metals contain positive ions surrounded by delocalised free electrons.
Metallic bonding is shown in the diagram. Ion A pulls left on the free electrons (green arrow). Ion B pulls right on the free electrons (red arrow). Like two kids fighting over a toy, the ions are held together.

The difference between yield and rate of reaction

This is bugging me a bit, but I think it boils down to this:

Yield means what percentage of the reaction ends up doing what you want. Remember that if it is a reversible reaction, it can make the product and then undo it again.

Rate of reaction means how fast the reaction goes; how quickly you get what you want.

Questions dealing with pressure be about either:

• If you increase the pressure you push the particles closer together so that they collide more often and the rate of reaction increases.
• If you increase the pressure of a reversible reaction involving gases, you favour the direction that goes from more molecules to less molecules. If that is the forward direction, then increasing the pressure will increase the yield.

It is the same with temperature:

• If you increase the temperature, the particle move faster and so collide more frequently. More collisions reach the activation energy. Hence the rate of reaction increases.
• If a reversible reaction is endothermic in the forward direction and you increase the temperature, then you will increase the yield.