Properties & Characteristics of Matter
Any characteristics that can be used to describe or identify matter are called a property. Some well-known properties are mass color melting point, boiling point, temperature etc.
Properties are often classified as either physical or chemical:
Physical properties- identify the substance without causing a change in its chemical composition. Alternatively it’s a property that can be measured without change of identity or composition. Examples are color melting point, mass density, electrical conductivity atomic or ionic size evaporation, condensation etc.
Chemical properties – one that can be observed only when the substance changes its chemical composition. In other words how a substance reacts with one another e.g. combustion, explosion, rusting.
Intensive / Extensive Properties of Matter
Properties of matter can also be classified as either extensive or intensive.
Intensive- has values that do not depend on sample size. This property helps to identify substances e.g. color b.p m.p taste odor, temperature, density.
Extensive- have values that depend on the amount of sample present e.g. mass, volume length etc.
Physical and Chemical Changes
Physical change- a change in the form or state of matter but in not in its chemical make-up.
- Dissolving salt in water. The water and the salt in the solution retain their chemical identities and can be separated.
- Melting ice to liquid water.
Chemical change – a chemical reaction, a change in the composition of the substances that takes place and a new and different substance is formed.
- Hydrogen and oxygen gas explode with a big bang when ignited producing water
- Enzymatic digestion of food by different enzymes
Chemical Composition of Matter
A sample of matter can also be classified based on its chemical composition.
Any sample of matter can be classified as either a pure substance or a mixture. A pure substance can either be an element or a compound.
Pure substance- has a fixed composition. It cannot be separated or purified into other kinds of substances by physical means. E.g. NaCl, H2O
Element- a substance that is comprised of only one type of atom. It cannot be chemically broken down into different simpler substances e.g. all the elements in the periodic table
Molecules – a substance formed when two or more atoms join together chemically e.g. iodine I2 or Water H2O
Compound – a substance composed of two or more different elements chemically combined or any pure substance that can be broken down by chemical means into two or more different, simpler substances e.g. NH3, H2O, Glucose.
A compound is a molecule that contains at least two different elements all compounds are molecules but not all molecules are compounds. Molecular hydrogen and molecular oxygen are not compounds because each is composed of a single element and cannot be broken down chemically into anything simpler. Water H2O, carbon dioxide CO2 and methane CH4 are compounds because each is made from more than one element. Water can be decomposed through electrolysis into hydrogen and oxygen gas.
Mixture – formed when two or more substances are mixed together in some random proportion without chemically changing the individual substances in the process, e.g. sugar in water, coke, fruit juices etc.
Law of Conservation of Mass – mass can neither be created nor destroyed; the total mass of the substances involved in a physical or chemical reaction remains constant.
e.g. During the rusting of a nail, the initial mass of the iron plus the mass of the oxygen combines to produce a mass of iron oxide (rust) equal to the sum of masses of iron and oxygen consumed.
Law of conservation of energy – energy changes can neither be created nor destroyed in a chemical process or physical change. It can only be converted from one form to another
Energy is the capacity or ability to do work or to transfer heat. E.g. light energy, electrical energy, and heat energy, mechanical and chemical energy.
Anytime a chemical reaction takes place, there is also a change in energy. Either energy is released by the reaction -exothermic reaction (e.g. metabolism) or energy is required to keep the reaction going – endothermic reaction (photosynthesis)