In the first post of the year, you’ll find attached multiple resources for CCEA AS1 Chemistry. These include a full set of revision notes on each topic.
The Collision Theory:
- In a chemical reaction, the reactant particles can only react with each other when they bump into one another. According to collision theory when molecules collide bonds between their atoms can break, and then new bonds can form to make new molecules.
- The molecules in gases and liquids are moving constantly, and millions of collisions take place every second. But only a small number of these collisions lead to the formation of product. For a collision to be ‘successful’, the particles involved must possess enough energy, called the activation energy, to break some of the existing bonds.
Measuring Rate of Reaction
- We can measure the rate of reaction using the following equation-
Factors Affecting the Rate of Reaction
Temperature- Increasing the temperature of a reaction speeds up the rate of reaction (increases the rate of reaction). The ions have more kinetic energy so they move about more and collisions occur more frequently. As there are more collisions, there are more successful collisions so the rate of reaction increases.
Concentration- Increasing the concentration of reactant liquids in a reaction also increases the rate of reaction. A high concentration means more particles per cm3 so there are more collisions per second which means there are more successful collisions so the reaction speeds up.
Surface Area- Increasing the surface area of a reactant solid increases the rate of reaction. A powdered substance always has a larger surface area than a block substance weighing the same amount. The more finely divided the solid is, the more of it is exposed to react with the other particles.
Catalyst- Use of a catalyst increases the rate of reaction. A catalyst is a substance that speeds up a reaction but is chemically unchanged. When the reaction finishes you have the same mass of catalyst. A catalyst provides an alternative route for the reaction, one with lower activation energy.
You may find the attachment useful. It covers the three types of bonding using short notes and bullet points. It’s really helpful to get the basics nailed down, and can help you understand bonding.
Hard and soft water
- Hard water is water that doesn’t lather easily soap. Soft water does lather easily with soap. Hardness in water is caused by dissolved calcium or magnesium ions.
- There are two types of hardness in water: temporary and permanent.
- Temporary hardness can be removed by boiling- permanent cannot.
- Temporary hardness is caused by dissolved calcium hydrogen carbonate.
- Permanent hardness is caused by dissolved calcium/magnesium sulphate or dissolved calcium/magnesium chloride.
- Calcium/magnesium ions in the hard water react with the soap to form scum.
Temporary Hard water: Limestone (CaCO3) reacts with rainwater containing dissolved carbon dioxide to form calcium hydrogen carbonate:
H2O (l) + CO2 (g) + CaCO3 (s) = Ca(HCO3)2 (aq)
Permanent Hard water: Rainwater dissolves rock containing calcium sulphate (Gypsum CaSO4). Because these compounds don’t decompose on heating, the calcium or magnesium ions remain in the water and it stays hard
CaSO4 (s) + aq = Ca2+ (aq) + SO42- (aq)
Softening Hard Water
1. Boiling (but only for temporary hard water):
Ca(HCO3)2 = CaCO3 (s) + CO2 + H2O
CaCO3 is insoluble in water and won’t cause hard water.
2. Adding washing soda: (hydrated sodium carbonate)
Dissolved calcium or magnesium ions are removed due to a reaction with carbonate ions from the washing soda to form insoluble CaCO3 (or MgCO3):
Ca2+ (aq) + CO32- (aq) = CaCO3 (s)
3. Ion Exchange:
Dissolved calcium or magnesium ions are removed and replaced by sodium ions from the ion exchanger
Advantages of Hard Water
- Tastes better
- Better for brewing beer
- Good for tanning leather
- It provides calcium for healthy bones and teeth.
Disadvantages of Hard Water
- Produces a scum with soap, which wastes soap
- It provides lime scale. This makes kettles less efficient and clogs up pipes.
If your doing a chemistry exam soon, then you may find the below list of definitions useful to you. There is also a section allowing you to revise what you’ve learnt afterwards.
Included in this post is a document containing many CCEA Past Papers from the last few years, with pointless pages removed and remaining joined together. You more than likely have a past paper booklet already, but I found it useful to print these papers out closer to the exam and repeatedly do them up to the exam. This will allow you to gain knowledge of how to answer questions and if you time yourself, how to deal with pressure.