Chemistry is a material science!

Define Chemistry

Chemistry is the study of matter: its composition, the changes matter undergoes, and the energy associated with these changes.

Definition

Matter is anything that has mass and takes up space, or has volume.

Matter Defined

This fundamental definition of matter leads to a common property of matter, namely, density. Density is equal to the mass divided by the volume.

Density: a spin-off

The “makeup” of matter is its composition. This answers the question what kind of atoms and molecules are present in this matter.

Composition

Matter composed of only one kind of particle such as an atom or molecule is a pure substance or simply a substance.

Substances

Substances are made of only one kind of element or compound.

Substances have physical properties such as melting and boiling temperature, solubility and density.

Physical Properties

Physical properties can be observed without changing the composition of matter. For example, copper wire can conduct electricity and remain copper.

Chemical properties deals with how a substance will react with another substance.

Neon gas is non reactive with all substances. Sodium metal is highly reactive and must kept under oil to prevent reaction with air or water.

The chemical property of a substance is basically its reactivity.

Physical properties that are the same regardless of the sample size are called intensive properties.

Intensive properties such as density and melting temperature can be used to identify the substance.

Extensive properties such as mass or volume will vary with the sample size.

Elements are composed of the same type of atom (same element e.g. Ne) or molecules of the same type of atom (element e.g. N2).

Compounds are composed of atoms of different elements in definite ratios. Carbon dioxide is CO2 and carbon monoxide is CO.

Mixtures are a combination of An element with element or Element with a compound or Compound with other compounds

Mixtures are a combination of substances with variable mass ratios.

Changes in matter can be classified as a physical change, a chemical change or a nuclear change.

Substances undergoing a physical change may have an alternate state of matter or change in shape, but never change in composition of the substance itself.

When H2O(l) as a liquid freezes it is H2O(s) as a solid, but there is no change is the fixed ratio of H:O in H2O. Thereby there is not change in the composition.

Chemical changes are called chemical reactions and are more difficult to reverse than physical changes.

In a chemical reaction new substances (called products) are formed with a new and different set of physical and chemical properties.

For example, when H2 and O2 react to form H2O. The H2O that extinguishes flames was produced from O2 that supports combustion and H2 that is highly flammable

Likewise the freezing and boiling temperature of both H2 and O2 is much lower than the corresponding freezing and boiling temperature of H2O.

A nuclear change releases the most of energy of all the changes. In nuclear reactions atoms of one element are often changed into atoms of different element.

Energy associated with changes.

Type of change in matter

Change in Energy

Physical Change

H2O(s) H2O(l)

334 joules needed

endothermic

Chemical Change

2H2(g) +O2(g) 2H2O(l)

285.8 kJ

exothermic

Nuclear Fusion3H + 2H4He + 1n

1.7 x 109 kJ

exothermic