Chemistry

Question 1

Signs there has been a chemical reaction:

Answer 1

• Release of energy (heat, light, sound)
• Permanent change of colour
• Formation of a precipitate

Question 2

Synthetic Materials

Answer 2

Synthetic materials, or man made materials, have been made, because most of the substances that appear naturally can no longer “support” human life as we know it. Chemical reactions are used to make synthetic materials.

Question 3

Physical and Chemical changes

Answer 3

Physical changes are changes in form or appearance, but its chemical structure does not alter. Many physical changes are reversible.

Chemical changes are changes in the chemical structure. These require some sort of energy for the atoms to rearrange themselves. It is very difficult to rearrange them back and those that do require perfect conditions in order to be reversed.

Question 4

Solid to liquid

Answer 4

Melting

Question 5

Liquid to gas

Answer 5

Evaporation

Question 6

Liquid to solid

Answer 6

Freezing

Question 7

Gas to liquid

Answer 7

Condensation

Question 8

Solid to gas, and vice versa

Answer 8

Sublimation. Gas to solid may also be known as deposition.

Question 9

Atoms

Answer 9

Atoms are the smallest possible particle, unless you include subatomic particles. They come from the ancient Greek word άτομος (atomos) meaning indivisible. This is because, they are, well, very hard to divide. Dividing atoms requires a lot of technology.

Question 10

Elements

Answer 10

Atoms have been named according to how many protons they have. They are called elements. Dmitri Mendeleev, a Russian scientist, designed the first periodic table of elements, a bit different from today’s periodic table.

Question 11

Compounds

Answer 11

Compounds are a combination of atoms joined together mainly via covalent or ionic bonds. They are different from mixtures in the way that compounds are homogenous and has a uniform structure, whereas mixtures are heterogenous and does not have a uniform structure.

Question 12

Behaviour of particles

Answer 12

Solid particles have strong bonds and have a definite shape and volume.

Liquid particles do not have a definite shape, but a definite volume.

Gas particles have weak bonds and have no definite shape and no definite volume.

Question 13

Properties of matter

Answer 13

Viscosity, refractive index, compressibility, hardness, heat capacity, conductivity, strength, density, freezing point, boiling point.

Question 14

Reactants and products

Answer 14

In a chemical equation, the reactants are on the left, followed by an arrow, indicating the reaction. Finally, the products are on the right. There can be more than one product, and there can be one reactant. Remember: Reactants react to produce products.

Question 15

Chemical and Physical Properties

Answer 15

Chemical properties include: Reaction with others, toxicity, coordination number, flammability, enthalpy of formation, heat of combustion, oxidation states, chemical stability, types of chemical bonds it will form.

Physical properties include: Appearance, texture, smell, solubility, colour, polarity.

Question 16

Volatility

Answer 16

How easy a substance can evaporate. Butane is a volatile substance.

Question 17

States of matter

Answer 17

Solid, liquid, gas, plasma. Remember them using the four elements: Earth (solid), water (liquid), air (gas) and fire (plasma).

Question 18

Matter

Answer 18

Matter is the result of atoms. Everything around us is matter. The trees, the cars, the sun, it’s all matter! The only thing that isn’t matter is a vacuum, or a void.

Question 19

Chemistry in real life

Answer 19

We need chemistry in order to make synthetic materials. Much of the things we have today are the result of a chemical reaction, and very rarely does an appliance at home occur “naturally.” Chemistry is required for medicine, for technology, and it even takes place in our bodies without us even noticing.

Question 20

Chemical equations

Answer 20

A chemical equation describes a chemical reaction. You need to use a capital letter for the first letter of the symbol, then a lowercase letter for the second letter, if there is one. This is for differentiation. One instance is Co (Cobalt) vs CO (Carbon Monoxide). You need to balance them, so the number of atoms on each side are equal.

Question 21

Periodic table

Answer 21

The periodic table is a table of all elements. On the periodic table includes the 118 elements, their atomic numbers, their atomic weight, its chemical type (metals, non metals, noble gases), its group number (1-18) and its period number (1-7). Each group of elements are different in properties. Each period shows how many shells an atom has.