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- 1. Multiple Choice
What is a chemical reaction?
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.
In it one or more substances, called reactants, are converted to one or more different substances, known as products. Substances are either chemical elements or compounds.
- 2. Multiple Choice
New substance is formed.
When iron and sulfur is heated a chemical reaction takes place I.e. Sulfur combines with the iron in the mixture in the presence of heat to form Iron sulfide (FeS).
Fe (Iron) + S (Sulphur) = FeS (Iron Sulphide)
- 3. Multiple Choice
The change is permanent and irreversible.
We can't reverse the change, it is permanent.
Example (Burning paper) - Fuel + O2 → CO2 + H2O
- 4. Multiple Choice
A change in the mass of the original substance .
The total mass of the reaction isn't changed but of a particular substance , it may change.
Example - Magnesium + oxygen → magnesium oxide.
2Mg + O2 → 2MgO
- 5. Multiple Choice
Exchange of energy takes place.
Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.
Example - A car changes energy stored in the chemical bonds of gasoline to several different forms.
- 6. Multiple Choice
Evolution of Gas.
Some chemical reactions are characterised by the evolution of gas.
Example - when sodium carbonate reacts with dilute hydrochloric acid evolution of carbon dioxide takes place.
Na2CO3 + 2HCl(aq) + 2NaCl(aq) + H2O(l) + CO2(g)
- 7. Multiple Choice
Formation of precipitate.
There are many chemical reactions which are characterized by the formation of precipitate.
Example - Reaction between silver nitrate and sodium chloride forms a white precipitate of silver chloride.
AgNO3 + NaCl + NaNO3 + AgCl
- 8. Multiple Choice
Change in color.
When titrations (a chemical reaction between acids and bases) are performed or during formation of metal oxides, the end point is observed by a color change.
Example - When citric acid reacts with potassium permanganate, the purple color of potassium permanganate disappears.
C6H2O, +3KMnO4 +3HMnO4 + C6H; K307
- 9. Multiple Choice
Change in temperature.
The reactions in which heat is evolved are called exothermic reactions and the reactions in which heat is absorbed are called endothermic reactions.
Example - When quick lime reacts with water then slaked lime is formed and energy is produced. This is an exothermic reaction.
CaO+H20 + Ca(OH)2
- 10. Multiple Choice
Change of state.
Some chemical reactions are characterised by change in state.
Example - When wax(solid) is burned, then water(liquid) and carbon dioxide(gas) are formed.
Fuel + O2 → CO2 + H2O
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