x Ch.1 Chemical reactions and equations key consents

1. Chemical reaction: A chemical reaction involves a chemical change in which substances react to form new substances with entirely new properties. Substances that react or take part in the reaction are known as reactants and the substances formed are known as products.
2. Physical change: If a change involves change in colour or state but no new substance is formed, then it is a physical change.
3. Chemical change: If a change involves formation of new substances, it is a chemical change.
4. Chemical equation: The symbolic representation of a chemical reaction is called a chemical equation.
5. Exothermic and endothermic reactions: If heat is evolved during a reaction, then such a reaction is known as exothermic reaction. If heat is absorbed from the surroundings, then such a reaction is known as endothermic reaction
6. Combination reaction: Combination reaction is a reaction in which two or more substances combine to give a single product.
7. Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
8. Displacement reaction: A reaction in which a more active element displaces less active element from its salt solution.
9. Reactivity series: The Reactivity series is a list of metals arranged in the order of decreasing reactivity. The most reactive metal is placed at  the top and the least reactive metal is placed at the bottom.
10.Double displacement reaction:  A chemical reaction in which there is an exchange of ions between the reactants to give new substances is  called a double displacement reaction.
11.Precipitation reaction: An insoluble solid known as precipitate is formed during a double is placement reaction. Such reactions are also known as precipitation reactions.
12.Redox reaction: A reaction, in which oxidation and reduction takes place simultaneously is known as redox reaction.
13.Oxidation: Oxidation is a chemical process in which a substance gains oxygen or loses hydrogen.
14.Reduction: Reduction is a chemical process in which a substance gains hydrogen or loses oxygen.
15.During a chemical reaction, there is a breaking of bonds between atoms of the reacting molecules to give products.
16. A chemical reaction can be observed with the help of any of the following observations:
a) Evolution of a gas               b) Change in temperature
c) Formation of a precipitate  d) Change in colour             e) Change of state
17. Skeletal chemical equation: A chemical equation which simply represents the symbols and formulae of reactants and products taking part in the reaction is known as skeletal chemical equation
for a reaction. For example: For the burning of Magnesium in the air, Mg + O2 → MgO is the skeletal equation.
18. Balanced chemical equation: A balanced equation is a chemical equation in which number of atoms of each element is equal on  both sides of the equation i.e. number of atoms of an element on
reactant side = number of atoms of that element on the product side.
19. As per the law of conservation of mass, the total mass of the elements present in the products of a chemical reaction is equal to the total mass of the elements present in the reactants.
20. Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
Types of decomposition reactions:
a. Decomposition reactions which require heat are known as thermolytic decomposition reactions
b. Decomposition reactions which require light are known as photolytic decomposition reactions
c. Decomposition reactions which require electricity are known as electrolytic decomposition reactions