science revision

Page 1

chemical energy & types of reaction:

Understanding Reactions:

exothermic: a chemical reaction that releases energy by light or heat

endothermic: a chemical reaction that takes in energy by light or heat

the difference between these two is that endothermic reactions absorb heat from the surroundings while exothermic reaction transfer energy to the surroundings

exothermic reactions cause the reaction mixtures and surroundings to become warmer while endothermic reactions cause it to become colder

EXAMPLES:

exothermic - burning, neutralisation between alkalis and acids, the reaction between water and calcium oxide

endothermic - electrolysis, the reaction between ethanoic acid and sodium carbonate, the thermal decomposition of calcium carbonate in a blast furnace

rule: "when chemical bonds are formed, heat is released, and when chemical bonds are broken, heat is absorbed"

Catalysts:

it's a substance which changes the rate of reaction (speeds it up) without being chemically involved.

additional info:

catalysts are specific to reactions

not all reactions have suitable catalysts

catalysts never produce more product - they just produce the same amount faster

the catalyst will not be affected in the end of the reaction as it not getting used up

reduces the energy needed to start a reaction (lower activation energy)

different catalysts work in different ways

Explaining changes:

substances can change state, usually when they are heated or cooled.

examples:

liquid water turns into steam when it is heated enough, and it turns into ice when it is cooled enough.

state changes are reversible – ice can be melted and then frozen again. no new elements or compounds are formed. the closeness, arrangement and motion of the particles in a substance change when it changes state.

during physical changes, the appearance of the product may look different from the reactant (original) but there are no new products.

LAW OF CONSERVATION OF MASS:

"the total mass of he product formed in a reaction is equal to the total mass of the reactants"

Combustion:

fuels are substances that react with oxygen to release useful energy. most of the energy is released as heat, but light energy is also released.

complete combustion needs a large supply of air so that the elements in the fuel react fully with oxygen.

fuels such as natural gas and petrol contain hydrocarbons. these are compounds of hydrogen and carbon only.

equation of complete combustion: hydrocarbon + oxygen → carbon dioxide + water

incomplete combustion occurs when the supply of air or oxygen is not enough. water is still produced, but carbon monoxide and carbon are produced instead of carbon dioxide. carbon monoxide is a poisonous gas, which is one reason why complete combustion is preferred to incomplete combustion.

equation of complete combustion: hydrocarbon + oxygen → carbon monoxide + carbon + water

the applications of combustion include: chemical reactions, heating devices, explosives, transportation

examples of fuels used in different applications:

burning logs on a fire = wood

car = petrol / diesel

Understanding thermal decomposition:

thermal decomposition reactions happen when substances break down to simpler products when they are heated. no new substances are added. many metal carbonates are decomposed on heating:

metal carbonate → metal oxide + carbon dioxide

applications of thermal decomposition:

limestone is mainly calcium carbonate, CaCO3. when it is heated, it breaks down to form calcium oxide and carbon dioxide. calcium oxide reacts with water to produce calcium hydroxide.

Limestone and its products have many uses, including being used to make mortar, cement, concrete and glass.

Page 2

evolution and inheritance:

Understanding the importance of biodiversity:

biodiversity - it is the variety of living things (plants, animals and microorganisms), their relationships and the ecosystems they live in

biodiversity is vital for supporting all life on earth. it ensures clean air and water, as well as fertile soil. every organism, no matter how small, has a part to play in what we call the 'balance of nature'. living organisms, rocks and soils, water and the atmosphere all interact to provide the conditions needed to sustain life on earth. if these ecological systems break down or change dramatically, life on our planet will be threatened.

example: the oceans play a major role in absorbing carbon dioxide from the atmosphere

an ecosystem with a high level of biodiversity is more able to survive changes, because there is a greater chance of one of the species having features that enable it to adapt to change this safeguards the system against the loss of other species, because the food webs were not affected.

tropical rainforests and coral reefs are the ecosystems with the greatest biodiversity on the planet.

Explaining extinction:

gene banks for animals and plants are vital for maintaining and preventing the loss of genetic diversity. this diversity is important for the survival wild animals and plants and also for the future of agriculture.

there are several causes (both environmental and human) hat can cause a species to become extinct. these include:

climate change - the biodiverse earth can't keep up with the rapid changes in temperature and species are not used to severe weather conditions and long seasons, or a changing chemical make-up of their surroundings. as more species die, it is only making it harder for the survivors to find food. the warmer climates are perfect to helping diseases and epidemics to thrive

changes in sea levels or currents - a small rise in he ocean floor can displace a lot of water onto land that is all ready occupied. the gases from the volcanic activity can also be absorbed by the water, thus changing the chemical composition, making it unsuitable for some life

acid rain - acid rain increases the acidity of the soil which affects plant life. it can also disturb rivers and lakes to a possibly lethal level

invading species - invasive species invade foreign territory. they use resources that the other species depend on. once competition gets too great, the survival of the fittest plan will begin, and one of the species, usually the natural one, will die off

Understanding the nature of genetic material:

the nucleus of every cell contains genetic information, which is arranged into chromosomes. these are thread-like strands made of a chemical called DNA. this chemical is divided into regions called genes. different genes control the development of different characteristics.

maurice wilkins began using x-rays to produce diffraction images of DNA molecules. the x-ray diffraction images produced by him, rosalind franklin, and raymond gosling led to the deduction by james watson and francis crick of the 3-dimensional helical nature of DNA.

heredity plays a key role in the development of traits and is transmitted through genes. the traits we inherit help shape our behavior, are determined by pairs of genes, one from each parent. genes are found in chromosomes, which are made of DNA.

Exploring the role of chromosomes:

all other cell types have 23 pairs of chromosomes, or 46 total. during meiosis, a cell undergoes two rounds of cell division during which the chromosome pairs are separated and the resulting gametes each have only one copy from each set of chromosomes. this is so when the sperm and egg combine during fertilization, the resulting zygote has 46 total chromosomes (or 23 pairs), 23 from the mother and 23 from the father.

genetic disorders can be caused by a mutation in one gene (monogenic disorder), by mutations in multiple genes (multifactorial inheritance disorder), by a combination of gene mutations and environmental factors, or by damage to chromosomes (changes in the number or structure of entire chromosomes, the structures that carry genes).

Page 3

wave effects and wave properties:

Comparing transverse and longitudinal waves:

transverse waves are those in which vibrations are at right angles to the direction of travel

longitudinal waves are those in which the vibrations are in the same direction as the direction of travel

frequency & amplitude:

the closer the waves (vibrations) are together the higher the frequency and the higher the pitch

pitch = frequency

the higher the wave the louder the volume

amplitude = volume

examples:

sound waves are longitudinal waves while light waves are transverse

key points:

amplitude is the height of a wave

wavelength is the length of one complete wave

frequency is the number of complete waves passing a single point per second

frequency is measured in hertz (hz)

energy is transferred in a wave but never particles

Uultrasound is a type of imaging. It uses high-frequency sound waves to look at organs and structures inside the body. health care professionals use it to view the heart, blood vessels, kidneys, liver, and other organs. during pregnancy, doctors use ultrasound to view the fetus.

Page 4

work and heating and cooling:

Doing work:

work is done whenever a force moves something. everyday examples of work include walking up stairs, or lifting heavy objects. whenever work is done energy is transferred from one place to another.

the difference between mass (g, kg) abd weight (newtons) is that weight is the force of gravity dragging you down and the mass is the amount of matter.

weight = mass x gravitational field strength

work done (joules, j) = force (newtons, n) x distance (metres, m)

examples:

what is the work done if we apply a 1.2n force and we move 4m in the direction of force?

1.2 x 4 = 4.8 j

what distance is moved if we have a 7n force and we move 8m in the direction of the force?

90 / 8 = 11.2 m

use the triangle below to help you rearrange the equation to:

force = work done / distance

distance = work done / force

Making work easier:

there are 6 basic simple machines; the lever, the wheel and axle, the inclined plane, the wedge, the pulley, and the screw. simple machines are useful because they reduce effort or extend the ability of people to perform tasks beyond their normal capabilities.

Explaining thermal energy & Energy and temperature:

the heat an object contains is the amount of its thermal energy, measured in joules or j. the temperate of an object is to do with how hot or cold it is, measured by a thermometer in degrees celsius.

adding ice to a glass of coke makes it cold, putting a kettle of water over a hot flame makes the water hot. whenever two objects of different temperatures are in contact, energy will transfer from the hotter object to the colder object. the energy transferred is called heat and the process is called heating.

the total amount of energy stored in the particles of an object is called its internal energy. temperature is a measure of the average kinetic energy of the particles. when an object is heated up, its particles gain more kinetic energy and hence its internal energy increases. A change in state will also result in a change in internal energy. When a liquid is changed to a gas, for example, the separation of its particles is increased greatly, leading to an increase in potential energy of the particles. Thus the internal energy of the object also increases. we cannot the measure the internal energy of an object directly. what we can measure is its change in internal energy. this may be equal to the amount of heat transferred to the object in the process of heating, or the energy supplied to the object in the processes of melting or vaporisation.