Maharashtra State Board · Class 10 · Chemistry · Chapter 3

Chemical Reactions and Equations — Formula Sheet

Board Formulas

12 formulas

1.Law of Conservation of Mass
$Mass of reactants = Mass of products$
Every balanced equation obeys this law — total atoms of each element are equal on both sides.
2.Combination Reaction★
$A + B \to A B$
Two or more reactants combine to form a single product. Example: 2Mg + O_2 → 2MgO.
3.Decomposition Reaction★
$A B \to A + B$
One reactant breaks down. Types: thermal (Δ), electrolytic (electric), photochemical (light).
4.Displacement Reaction
$A + B C \to A C + B$
More reactive metal displaces less reactive one. Zn + CuSO_4 → ZnSO_4 + Cu.
5.Double Displacement
$A B + C D \to A D + C B$
Two salt solutions exchange partners. Often produces a precipitate or gas.
6.Precipitation Example
$B a C l_{2} + N a_{2} S O_{4} \to B a S O_{4} ↓ + 2 N a C l$
White precipitate of barium sulphate — a classic double-displacement (precipitation) test.
7.Thermal Decomposition of Calcium Carbonate
$C a C O_{3} Δ C a O + C O_{2} ↑$
Basis of lime production. CaO = quicklime.
8.Electrolysis of Water
$2 H_{2} O electricity 2 H_{2} ↑ + O_{2} ↑$
Volume ratio at cathode : anode = 2 : 1 (H_2 : O_2).
9.Photodecomposition of Silver Chloride
$2 A g C l light 2 A g + C l_{2}$
White AgCl turns greyish — basis of black-and-white photography.
10.Thermite Reaction (Redox)★
$F e_{2} O_{3} + 2 A l \to 2 F e + A l_{2} O_{3} + heat$
Highly exothermic — molten Fe used to weld broken rails.
11.Oxidation and Reduction
$Oxidation: loss of electrons; Reduction: gain of electrons$
OIL RIG — Oxidation Is Loss, Reduction Is Gain.
12.Photosynthesis (Endothermic)
$6 C O_{2} + 6 H_{2} O sunlight C_{6} H_{12} O_{6} + 6 O_{2}$
Energy from sunlight is absorbed — an endothermic reaction.