Definitions [15]
The substances taking part in chemical reaction are called reactants.
Define electrolysis.
The cell which converts electrical energy into chemical energy is called an electrolytic cell and the process which converts electrical energy into chemical energy is called electrolysis.
Define a photochemical reaction.
A chemical reaction that occurs in the presence of light is called a photochemical reaction.
Define catalyst.
A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.
Define chemical reaction.
Any chemical change in matter that involves its transformation into one or more new substances is called a chemical reaction.
Define an electrochemical reaction.
An electrochemical reaction is a chemical reaction involving the transfer of electrons, where oxidation and reduction occur simultaneously.
Define the following term:
Precipitate
Chemical reactions which are characterised by the formation of insoluble solid substances are called precipitates.
Define precipitation reaction.
A chemical reaction in which two compounds in their aqueous state react to form an insoluble salt as one of the products.
Define the following term:
Chemical change
A chemical change is a permanent change in which the chemical composition of a substance is changed and one or more new substances with different chemical compositions and different properties are formed.
The substances formed as a result of a chemical reaction by formation of new bonds are called products.
A chemical change is a process in which the composition of matter changes, resulting in the formation of one or more new substances.
Define the following terms
Chemical bond
A chemical bond is the force which holds the atoms of a molecule together as in a compound.
Define the following terms:
Effervescence
Formation of gas bubbles in a liquid during a reaction is called effervescence.
A chemical equation is a balanced account of a chemical transaction. It is not merely a qualitative statement, but it also gives quantitative information of a chemical reaction.
OR
The representation of a chemical reaction in a condensed form using chemical formulae is called as the chemical equation.
Define: Endothermic reaction
The reactions in which heat is absorbed are called endothermic reactions. The reactants absorb heat for form products.
Formulae [1]
What do you observe when iron nail is kept in copper sulphate solution for sometime.
When an iron nail is kept in copper sulphate solution, a reddish brown coating is seen on the iron nail after sometime. Also, the colour of the copper sulphate solution changes from blue to green. This is observed because iron displaces copper from copper sulphate solution, as iron is more reactive than copper.
\[\ce{Fe_{(s)} + CuSO4_{(aq)} -> FeSO4_{(aq)} + Cu_{(s)}}\]
Key Points
- Word equations use names; chemical equations use formulas.
- Reactants → Products, with arrow showing reaction direction.
- Use + between two or more reactants or products.
- Show states: (s), (l), (g), (aq); use ↑ for gas, ↓ for precipitate.
- Heat (Δ) or other conditions go above/below the arrow.
- Law of Conservation of Mass: In a chemical reaction, mass is neither created nor destroyed, so the number of atoms of each element must be equal on both sides.
- A skeletal (unbalanced) equation has unequal atoms of one or more elements on the LHS and RHS.
- Balancing is done using the hit-and-trial method, starting with the compound having the most atoms and balancing hydrogen and oxygen last.
- Only coefficients are changed while balancing; chemical formulas must not be altered.
- A balanced equation may also indicate physical states (s, l, g, aq) and reaction conditions, such as temperature, pressure, or a catalyst.
