Kinetic theory of matter
1.Matter is made up of tiny, invisible moving particles.
2.Particles of different substances have different sizes.
3.Lighter particles move faster than heavier ones at a particular temperature.
4.As the temperature rises, the particles move faster. As the temperature decreases, the particles move slower.
The 3 states of matter are solid, liquid and gas.
SOLIDS- have restricted movement- rotation and vibration only. The particles are closely packed and held together by forces of attraction. Solids have a definite volume and shape.
LIQUIDS-have less restriction of movement- they have greater rotational and vibrational movement and some translational movement.
They can slide past each other. There is still enough attraction between particles to maintain a definite volume.
A liquid takes the shape of the container in which it is placed.
GASES- have greater freedom of movement. Gas molecules are in a constant state of random motion. They are separated by large distances and travel with great speed- they will often collide with each other.
A gas will alter both its shape and volume to fill a container completely.
Change of state
An increase or a decrease in kinetic energy leads to a change of state.
–Evaporation – conversion of liquid into gas.
–Condensation – conversion of gas into liquid.
–Melting – conversion of solid into liquid.
–Freezing – conversion of liquid into solid.
–Sublimation – direct conversion of a solid to a gas or a gas to a solid.
A chemical reaction has taken place if at least one new substance has been formed.
A chemical equation can be written for chemical reactions.
Eg. REACTANTS --> PRODUCTS
Signs of chemical reactions include:
Formation of a precipitate, formation of a gas, colour change, energy absorbed or lost.
TYPES OF CHEMICAL REACTIONS
*Precipitate- when an insoluble solid forms when two or more clear (not always colourless) solutions are mixed.
*Exothermic- these reactions release heat- the temperature increases.
*Endothermic- these reactions absorb heat- the temperature decreases.
*Redox- where electrons are lost or gained in a reaction.
*Combination- where two or more substances combine to form a new substance.
•Eg. Carbon + oxygen --> carbon dioxide
C + O2 --> CO2
*Decompostition-where a single substance is broken down into simpler substances or elements.
Eg. Copper carbonate --> copper oxide + carbon dioxide
CuCO3 --> CuO + CO2
*Single replacement involves removing one element or group of elements and replacing them with another element or group of elements.
Eg. Copper + silver nitrate --> silver + copper nitrate
Cu + 2 AgNO3 --> 2 Ag + Cu(NO3)2
*Double replacement reaction- involves two metal ions swapping to form two new compounds. (Sometimes a precipitate is formed here).
Eg. Barium nitrate + Copper sulfate --> copper nitrate + Barium sulfate
Ba(NO3)2 + CuSO4 --> Cu(NO3)2 + BaSO4
*Neutralisation- where an acid reacts with a base to produce a salt and water.
ACID + BASE --> SALT + WATER
Eg. hydrochloric acid + sodium hydroxide --> sodium chloride + water.
*Acid and a carbonate base- If the base added during neutralisation contains a carbonate, then the following reaction occurs:
ACID + CARBONATE BASE-->SALT + WATER+ CARBON DIOXIDE
Eg. hydrochloric acid + sodium bicarbonate --> sodium chloride + water + carbon dioxide
*Metal and an Acid-An acid will react with a metal to produce a salt and hydrogen gas.
ACID + METAL -->SALT + HYDROGEN
Eg. Hydrochloric acid + Magnesium --> magnesium chloride + hydrogen.
BALANCING CHEMICAL EQUATIONS
•Chemical formulas- are a shorthand representation of compounds showing the ratios of each element in the compound.
•Chemical equations- show what is reacted and what is produced along with the formula of each substance.
•Eg. CuCO3 --> CuO + CO2
•Balanced chemical equations- here the numbers of atoms on one side of an equation must equal the number of atoms on the other side of the equation (conservation of mass).
Zn + HCl --> ZnCl2 + H2
1 Zn 1H 1 Cl 1 Zn 2Cl 2 H
Thus, to balance we need to multiply HCl by 2 to get 2 hydrogen atoms and 2 chlorine atoms.
Zn + 2 HCl --> ZnCl2 + H2
Balancing chemical equations is a skill related to an area of Chemistry known as STOICHIOMETRY- which deals with the quantitative (measuring) aspects of chemistry.
Physical states- symbols are added to show the physical states of the reactants and products.
Liquid – (l)
Gas – (g)
Aqueous (water) solution- (aq)
Diagram courtesy of By Yelod - Wikimedia Commons * Yelod - Wikipedia (En) * ילוד - ויקיפדיה העברית - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7719358
Changes of state diagram courtesy of E. Generalic, http://glossary.periodni.com/glossary.php?en=states+of+matter