Recently in science we have been learning about energy changes in reactions and addition polymerisation.
Energy changes in reactions
When a chemical reaction occurs, energy is transferred from or to the surroundings. After this has happened, there is often a temperature change. There are two types of reactions, they are: endothermic reactions and exothermic reactions.
Exothermic reactions are reactions that transfer energy to the surroundings. Exothermic reactions result in a temperature increase. Examples of exothermic reactions are:
• Neutralisation reactions between acids and alkalis.
• The reaction between water and calcium oxide.
Energy is either taken in or given out during a chemical reaction. During an exothermic reaction, energy is given out. When the energy is given out it means the products have less energy than the reactants, this can be shown using an energy-level diagram. During an endothermic reaction, energy is taken in. If it’s an endothermic reaction the products will be higher than the reactants. Below is an energy level diagram showing endothermic reactions.

Addition polymerisation
Polymers are large chain of monomers joined together. Monomers are simple molecules that make up Polymers. Alkenes (methane, ethene, propene and butene) are able to act as monomers because they contain a double bond. They join end-to-end during the reaction called polymerisation. They polymers they form are called ‘addition polymers’.
The equation for addition polymers = a lot of monomers → a polymer molecule
Example 1 – with detail
Let’s start with propene and polypropene. The reaction which will take place is:
• Propene → poly(propene)

Shown below is the displayed formula for propene. In the previous blogs you should of have read how to draw and work out the displayed formula for alkenes. As you can see propene has 3 carbon atoms and 6 hydrogen atoms. The first carbon atom has 2 hydrogen atoms and is connected to a double bond which leads on to the next carbon atom with 1 hydrogen atom, then from there the final carbon atom which contains the final 3 hydrogen atoms.

Also below is the displayed formula for propene → poly(propene). As you can by the diagram to make the reaction propene → poly(propene), you have to take the propene molecule and bunch 1 carbon atom and 3 hydrogen atoms together to make CH3. After you have done that, to make the poly(propene), you take the exact same displayed formula as propene but this time you have to remove the double bond and put brackets around the formula. Once you have put the brackets in you then put a little n on the outside of it.

Shown below is the addition polymerisation reaction of polychloroethene

Uses of polyethene include:
• Material of plastic bags
• Material of dustbins
• Material of washing up bowls
• Clingfilm
• A drink bottles
• Strong material
• Easy to shape (malleable)
• Transparent

Uses of polypropene include:
• Material of certain floor tiles
• Milk bottles
• Making cable ties
• Very strong material
• Stronger than Polyethene
• More rigid than Polyethene

Questions based on these topics.
1. If you have a negative value what type of reaction do you get?
2. If you have a positive value what type of reaction do you get?
3. What is polymerisation?
4. What makes up polymers?
5. What is a monomer?
6. If you have Polybutene, what does polymerisation turn it into?
7. If you have chloroethene, what does polymerisation turn it into?
8. What does exothermic mean?
9. What does endothermic mean?
10. What term is used when describing the starting chemicals in a reaction?
Answers
1. An exothermic reaction.
2. An endothermic reaction.
3. Polymerisation is the reaction that makes polymers.
4. Long chains of monomers make up Polymers.
5. A monomer is a single molecule.
6. Butene.
7. Polychloroethene.
8. Exothermic is an increase in temperature.
9. Endothermic is a decrease in temperature.
10. Reactant.

This week in triple science we have learnt about polymers and the structure of DNA. On Monday we learnt about polyesters. We also learnt about condensation reactions. Condensation reactions is a reaction in which two small molecules react form a larger molecule, with the elimination of water. To make a polyester by condensation you will need to draw out separately your diacid (which is a dicarboxylic acid) and your diol (which is your alcohol). You would then take away two of the H’s s and one O you take these away because they are lost to make water. After you have taken the water away you join the two together to make a polyester but you have to put a big bracket around each of then ends and draw lines through the bracket this is to show that the polyester and then be bonded on to other polyesters then you have to put a lowercase “n”. An example of how you lay it out is shown below. An example of a condensation reaction is of propanediol and butanedioic acid.

On Thursday which was our next triple science lesson we learnt about the structure of DNA. We learnt that DNA is made up of two strands and that it is made up of monomers known as nucleotide. The shape of a DNA strand is a double helix. We also learnt that there are four different nucleotides these are known as Adenine, guanine, thymine and cytosine. Adenine pairs with thymine. guanine pairs with cytosine. For example, if strand 1 was ATGGCATAGGCAT then strand 2 would be TACCGTATCCGTA. We also learnt about the structure of the DNA strands. This is a DNA strand example and what each piece breaks into

We also learnt that each 3 bases = triplet. Each triplet codes for a different amino acid. Each amino acid makes a different protein. Genes code for protein, proteins are made up of amino acids. Genetic codes are degenerate as more than 1 triplet can code for an amino acid. On Friday we did some revision on different topic in biology and created flash cards with the question and answers on them. Some of the questions were:
List the different organelles in a plant and their functions?
Nucleus- where DNA is found and controls the cell
Vacuole- stores water
Ribosomes- makes protein
Cell wall-supports the shape of the cell
Cell membrane- allows substances In and out of the cell
Chloroplast- where photosynthesis happens
Mitochondria- releases energy. site of aerobic respiration
Cytoplasm-where chemical reactions occur
Another question was:
What is active transport?
Active transport is where substances need to be absorbed against a concentration gradient from a low concentration to a high concentration. Active transport requires energy and a protein carrier. Happens across a partially-permeable membrane.