My Reflection

Reflection

When I saw the topic “chemical changes”, I thought it was a easy topic but after I went to research more, I realized it was hard and there are a lot of types of chemical changes, like electrolysis, decomposition, combination, cracking, photosynthesis, combustion and many many more. Luckily my mom was there to help me she took out five books about chemistry and told me that they would help me with my project, I started by finding out the types of chemical changes and then grouped them. Then using the textbooks my mom gave me, I did more background research, but most were hard and I had to rely on my mom to explain it to me. In the end, I finished the entire thing and now doing the report.

One question that occurred to me is “what is the difference between combustion and oxidation?” In my research, in oxidation, magnesium burns in air and the magnesium will be oxidised by the oxygen, but yet it also combustion describes the chemical reaction where the magnesium reacts with oxygen in an exothermic reaction. So it makes me wonder what is the difference between these two chemical changes, combustion or oxidation? Another question is photosynthesis is endothermic which means it takes in heat energy for photosynthesis to occur, but photosynthesis takes place when the chloroplast takes in sunlight. So why is photosynthesis an endothermic reaction when it takes in sunlight??Another question is “Why is respiration considered a chemical reaction that involves heat?”, respiration is only the exchange of gases in the lungs. Another question is will a strong acid be neutralized by a weak acid ? and vice versa.

I encountered a few difficulties in the project and that is understanding everything in the book or in the web. Most of the information were very hard to understand because those information must be for more advanced students. Other difficulties like the information from different websites were different therefore making me confused. I solved it by checking different websites to make sure my information was correct. Another difficulty is time and because the examination was a week away, we had to both study and do this project( this project is twenty percent of the mastery review), so we had to plan our time very well or else the project and the studying would not be completed. Another difficulty is that there are so many types of chemical change that it is so difficult to put everything into the glog, so I just took out a few main ones and just researched on them

From this I learnt how to plan my time well, paraphrase paragraphs that were too long or to prevent plagiarism .I also feel that this project is very good because a lot of us will learn new things, it also increase our information on our topic so that we are more prepared on that certain topic during the exam. This project also is good because we have to do our own reflection as reflection is important or you might as well copy paste and not learn anything.

References

1)longman complete guide to 'o' level chemistry book

2)Science in focus chemistry for GCE 'o' level

3)Chemistry matters teacher's edition workbook

4)Lower secondary science (EPH)

5)http://www.answers.com/

6)http://www.ric.edu/faculty/ptiskus/chemical/

7)http://www.mcwdn.org/chemist/pcchange.html

8)http://chemistry.about.com/od/lecturenotesl3/a/chemphyschanges.htm

Glossary......

endothermic==================>Characterized by or causing the absorption of heat

exothermic===================>Releasing heat

magnesium===================>A light, silvery-white, moderately hard metallic element that in ribbon or powder form burns with a brilliant white flame.

alkane=======================>Any of a class of hydrocarbons whose molecules consist only of carbon and hydrogen atoms joined by single covalent bonds

carbonate====================>A salt of carbonic acid.

chloride======================>A binary compound of chlorine

hydrocarbons=================>Any of numerous organic compounds, such as benzene and methane, that contain only carbon and hydrogen.

reducing agent================>A substance that chemically reduces other substances, especially by donating an electron or electrons.

CHEMICAL CHANGES INVOLVING HEAT

Respiration

Respiration is the release of energy from glucose or another organic chemical, the chemical energy from the glucose will be used to provide the energy needed for growth, repair and movement.

Examples of respiration is when oxygen diffuses out of the air in the lungs into the blood, and carbon dioxide diffuses out of the blood into the air in the lungs.

Another example is when every cell in the body "burns" sugar in the presence of oxygen to make ATP, the form of energy used in the cell, carbon dioxide and water are the by-products.

This reaction is exothermic because it produces energy.

CHEMICAL CHANGES INVOLVING LIGHT

Photosynthesis

Chlorophyll absorbs sunlight then photosynthesis turns carbon dioxide, water and sunlight into carbohydrate molecules.These carbohydrates are used by all living things as fuel for energy, and as building blocks to build more pieces of themselves.

The reaction of photosynthesis utilizes six carbon dioxide molecules and six water molecules to produce one sugar molecule (glucose) and six oxygen molecules.

Photosynthesis is the process by which plants and some single-celled organisms produce sugars from sunlight and carbon dioxide. These sugars then become the food used in cellular respiration. In plants, photosynthesis occurs in specialized structures known as chloroplasts.

This reaction is endothermic because it takes in light energy.

CHEMICAL CHANGES INVOLVING HEAT

Cracking

This process involves big molecules of hydrocarbon(alkane) are broken up into smaller molecules in the presence of a catalyst at a high temperature.

An example of cracking is when big petroleum molecules are broken up into smaller hydrocarbon molecules to produce fuel for motor vehicles, most of the fuel used in vehicles is produced by cracking.

Another example is a big alkane molecule breaks down into an alkane molecule and an alkene molecule.

This is a exothermic reaction because energy is needed to break the molecule.

CHEMICAL CHANGES INVOLVING LIGHT

Photography

In photography, photographic films have silver bromide crystal coating. In the presence of light, silver bromide crystals form into silver atoms. Silver bromide crystal wich have not been exposed to light are removed by dissolving in a solution called "fixer".

The film is now called a "Negative", the opaque parts have been exposed to lights while the transparent parts are not exposed to light. When the film is exposed to light, the photograph will be formed.

This is an endothermic reaction where energy is absorbed(light energy).

CHEMICAL CHANGES INVOLVING ELECTRICITY

Electrolysis

It is the process whereby compounds which conduct electricity undergo chemical change during conduction. Compounds which conduct electricity and undergo electrolysis are called electrolytes.In electrolysis, electrical energy is converted into chemical energy.

An example is : Oxygen and hydrogen are produced when water goes through electrolysis.

This reaction is endothermic because bonds are broken.

CHEMICAL CHANGES INVOLVING MIXING

Reaction between a metal and an acid

This occurs when dilute acids react with metals to form a gas called hydrogen

An example is when magnesium and hydrochloric acid react together and magnesium chloride and hydrogen is formed.

Another example is sulfiric acid and calcium will combine to calcium sulfate and hydrogen gas.

This is an exothermic reaction as heat is given out.

Reaction between an acid and a metal carbonate

This occurs when a metal carbonate and an acid form a gas called carbon dioxide.

An example is when hydrochloric acid is mixed with calcium carbonate, it will form calcium chloride, carbon dioxide and water.

This is also an exothermic reaction as heat is given off.

CHEMICAL CHANGES INVOLVING MIXING

Neutralisation

Neutralisation is a process whereby a base reacts with an acid to form salt and water only.This means that the acid has lost its acidic properties.

Like an example, when sulfuric acid is mixed with magnesium oxide the end product are magnesium sulphate and water.

Another example is when hydrochloric acid is mixed with sodium hydroxide, the mixture will become sodium chloride and water.

This is an exothermic reaction as heat is produced.

CHEMICAL CHANGES INVOLVING HEAT

Combustion

Combustion is also a chemical change involving heat.

Combustion describes the chemical reaction where some substances react with oxygen in an exothermic reaction ( that is heat is produced). If flames are produced during combustion, it is called burning.

Example when magnesium is burnt in oxygen, a new product will be formed and heat is produced. The new product formed by the magnesium and oxygen is magnesium oxide.

Hydrocarbons are fuels which are burnt to produce energy.Hydrocarbons are compounds that consist of carbon and hydrogen. Example, when it is burned in oxygen, it produces carbon dioxide and water.

This is an exothermic reaction as heat is produced.

CHEMICAL CHANGES INVOLVING HEAT

Oxidation and and Reduction

Oxidation and Reduction are chemical reactions that involve heat.

Oxidation describes those chemical reactions in which:

(a)hydrogen is removed from the substance.

(b)oxygen is added to the substance.

(c)the substance loses electrons.

Reduction describes those chemical reactions in which:

(a)hydrogen is added to substance.

(b)oxygen is removed from the substance.

(c)the substance gains electrons.

1)An example is magnesium burn s in air, magnesium is oxidised by the addition of oxygen, and oxygen is reduced. The oxygen is the oxidising agent while magnesium is the reducing agent.

2)another example is : zinc dissolves in dilute hydrochloric acid. Zinc is oxidised by the addition of chlorine and hydrogen is reduced. The chlorine ions are neither oxidised or reduced. Zinc is the reducing agent while the hydrogen ions are the oxidising agent.