1.Most Metals react with Oxygen to form Metal Oxide
For Example-:
- 2Mg + O2 → 2MgO
- 2Ca + O2 → 2CaO
- 4Na + O2 → 2Na2O
- 4K + O2 → 2K2O
2. Characteristics of Chemical Reactions
When a chemical reaction takes place, many types of things happen. such as-
- Evolution of a gas
- Formation of a precipitate
- Change in colours
- Change in temperature
- Change in state
Reactions for Evolution of Gases
Most metals react with acid to form metal salt with evolving hydrogen gas. such as-
- 2Na + H2SO4 → Na2SO4 + H2
- 2K + H2SO4 → K2SO4 + H2
- Zn + H2SO4 → ZnSO4 + H2
- Mg + H2SO4 → MgSO4 + H2
Most of the metal carbonates or metal bi-carbonates react with acid to evolve carbon di oxide gas.
- Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
- K2CO3 + H2SO4 → K2SO4 + CO2 + H2O
- CaCO3 + HCl → CaCl2 + CO2 + H2O
Reactions for the formation of Precipitate(insoluble part)
A precipitate is a “solid product” which separates out from the solution during a chemical reaction.
Potassium iodide reacts with lead(II) nitrate and produces lead(II) iodide and potassium nitrate. Potassium nitrate is water-soluble. However, lead(II) iodide is only partially soluble in water. … The lead ions and iodide ions will eventually meet to form a yellow precipitate.
2KI + Pb(NO3)2 → 2KNO3 + PbI2 (.ppt)
When solutions of sodium chloride and silver nitrate are mixed, then a white solid (silver chloride) formed.
NaCl + AgNO3 → AgCl(ppt) + NaNO3
Reactions for change in color during a chemical reaction
Copper reacts with moist CO2 to give copper carbonate, which changes color from brown to blue or blue-green. rusting, blackening of surfaces of cut vegetables and fruits are other examples of change of color in a chemical reaction.
- 2Cu (brown) + O2 → 2CuO(blue-green)
- CuO + CO2 → CuCO3 (green color)
When we heat ZnCO3 (white color) then we get the yellow color of ZnO substance.
ZnCO3 (white)→ ZnO(yellow) + CO2
Reactions for change in temperature during Chemical process
During chemical process, temperature or thermal energy may be increased or decreased in a chemical reaction.
- When quicklime(CaO) reacts with water(H2O), slaked lime(Ca(OH)2) is formed with a release of a large amount of heat, causing the change in temperature in the reaction mixture.
- CaO + H2O → Ca(OH)2 + Heat Energy (temperature increased)
- When baking soda(NaHCO3) is mixed with vinegar(CH3COOH), something new is formed. The mixture quickly foams up with carbon dioxide gas. Sodium bicarbonate and acetic acid react to carbon dioxide, water, and sodium acetate.
- NaHCO3 + CH3COOH → CO2 + H2O + NaCH3COO (temperature decreased).
Changing in the state into a chemical reaction
Some reactions changes their physical reactant’s state in the form of product.
- C (solid) + 2S (solid) → CS2(gas)
- NH3(gas) + HCl(aqueous) ⇌ NH4Cl (solid or crysattaline solid)
- 2H2(gas) + O2(gas) → 2H2O (liquid)
- 2H2O(liquid) → 2H2 (gas) + O2(gas)