Concept of Basic Chemistry

Objectives After this session, the students are expected to be able to: explain the difference between atom, molecule and material 3. explain chemical reaction 2. explain the law of conservation of mass Teknologi dan Rekayasa

Atomic theory Dalton’s atomic theory: 1. All matters are composed of atoms which are indivisible 2. All the atoms given of an element are alike in weight and in all other respect 3. The atoms of different elements are difference of weights 4. Atoms are indestructible and preserve their identities in all chemical reactions Teknologi dan Rekayasa

The nature of element The proportion by weight of the elements present in any chemical compound are entirely independent of the manner in which the compound is prepared If two elements A and B combine to form the two-atoms molecule Teknologi dan Rekayasa

Molecule If two elements A and B combine to forms various compounds and if the weight of element A in each compound is kept constant, then the weights of element B present in these compounds will be in the ratio of small integers Teknologi dan Rekayasa

Molecule For example that water is a binary compound of hydrogen and oxygen and the relative weights of the two elementary atoms are 1 : 7 Teknologi dan Rekayasa

Material If two compounds are mixture become a material For example mixture of iron powder with sulfur become a new material Teknologi dan Rekayasa

Chemical Equation Any chemical reaction can be represented by an equation that shows as all reactants and products and their physical states The physical states are shown by the use of the letters s, l, g for solid, liquid and gas respectively Teknologi dan Rekayasa

Chemical Equation These letters are placed in brackets after the appropriate chemical formula For example, the decomposition of ammonium nitrate can be represented as : NH4NO3 (s) → N2O (g) + 2 H2O (l) …(1) This equation states that 1 mol of solid NH4NO3 reacts to give 1 mol of gaseous N2O and 2 mol of liquid water Teknologi dan Rekayasa

Chemical Equation Substances that are presented in aqueous solution can be indicated by the use of ‘aq’ for aqueous, as in the equation : Ag+ (aq) + Cl– (aq)  AgCl (s) …..(2) This equation states that 1 mol of Ag+ in aqueous solution and 1 mol of Cl– in aqueous solution react to give 1 mol of solid AgCl Teknologi dan Rekayasa

Law of Conservation of Mass The above examples are balanced equation. This means that the same number of atoms of each element appears on each side of equation For example, the first equation has three oxygen atoms on the left side and three on the right This is in agreement with the Law of Conservation of Mass Teknologi dan Rekayasa

Electrolytes Many substances when dissolved give solution that conduct electricity readily, whereas other do not Those substances that give conducting solutions are called electrolytes and now are known to give free ions in solution Solvents like water, alcohols and various organic substances dissolves many electrolytes readily Teknologi dan Rekayasa

Stoichiometry Definition : Stoichiometry is the study of the quantitative relations between amounts of reactants and amounts of products in chemical reactions It allows us to calculate how much of one chemicals is needed to form another Teknologi dan Rekayasa

Chemical reaction Characteristic of chemical changes: * Temperature changes (Exoterm & Endoterm) *Colour change * Precipitated formation * Gases formation Teknologi dan Rekayasa

Physical changes Melting Freezing Sublimation Condensation Evaporation Deposition Teknologi dan Rekayasa