1st year Chemistry Chapter 1 Introduction to Fundamtal Concepts of Chemistry Question an Answers
Short and Simple Question an Answer
Q.1: Give reasons that formation of positive ion is in endothermic reaction?
Ans: Formation of positive ion is an endothermic process because heat is required to remove electron from a neutral atom to form positive ion.
Q.2: Why a physical change is temporary change?
Ans: Because due to the physical change no new substances are formed, therefore it is temporary change.
Q.3: Explain why chemical change is permanent change?
Ans: As during chemical change new substances are formed so it is a permanent change.
➤ Rusting of iron.
➤ Conversion of water in a steam.
Q.4: Why a limiting reactant controls the quantities of products in a chemical reaction?
Ans: The limiting reactant is a substance which produces least of products after its complete consumption. After the complete consumption of the limiting reactant no more products are formed, as the reactants are not mixed in stoichiometric amounts to form products. During a chemical reaction. Thus a limiting reactant controls the quantities of products in a chemicle reaction.
Q.5: what is the atomic mass unit?
Ans: It is a unit of mass used for atoms and molecules and it equal to the 12 of the mass of carbon atom – 12. It is obtained by dividing the unity by Avogadro’s number (6.02 x 1023).
Q.6: Define empirical formula and explain how it is related to molecular formula?
Ans: The simplest formula of a substance which tells us the ratio of atoms in the molecule of a substance is called empirical formula.
MF = n(E.F)
Q.7: Why molecular formula is the multiple of empirical formula? Give one example?
Ans: The empirical formula is the simplest whole number ratio of atoms of different elements present in a compound. Molecular formula tells us the number of atoms of each element in a molecule. Hence the empirical formula has to be multiplied with a suitable digit to get the molecular formula.
Q.8: N₂ and CO have same number of electrons, protons and neutrons. Justify?
Ans: In N₂:
No. of electrons in N₂ = 7+7=14
No. of protons in N₂ = 7+7=14
And No. of neutrons in N₂ = (14-7)=7+7=14
No. of electrons in C=6
No. of electrons in 0=8
Total number of electrons = 6 +8=14
Number of protons in C=6
Number of protons in 0=8
Total number of protons 6 + 8 = 14
Number of neutrons in C = 6
Number of neutrons in 0=8
Total number of neutrons = 6 + 8 = 14
Q.9: How can the efficiency of a chemical reaction can be expressed?
Ans: The efficiency of a chemical reaction can be expressed by the percentage yield of the chemical reaction. Percentage yield depends upon the ratio of actual yield and theoretical yield.
Yield (%) = Actual Yield / Theoriical Yield × 100
Q.10: Distinguish between actual and theoretical yield?
Ans: The amount of the product that is obtained in a chemical reaction is called actual yield. The amount of product calculated from balanced chemical equation is called theoretical
The efficiency of the chemical reactions can be calculated as
Yield (%) = Actual Yield × 100 P / Theoretical Yield
Q.11: What is limiting reagent? How it helps to control the reaction?
Ans: A limiting reagent is that one, which is in lesser quantity and it is consumed earlier.
Whenever, it is consumed then the further formation of the product stops, although then
excess reagent is lying in the vessel if the limiting reagent is not available to the excess
reagent then product can be found further.
Q.12: Whenever an electron is removed from the atom a cation is produced and the formation of the cation is au endothermic process. Why?
Ans: The number of electrons and protons in an atom are equal. When the electron is removed from the atom, energy has to be supplied. So it is an endothermic process. The ion developed from the positive charge and is called action.
Q.13: Why the isotopes have the same chemical properties?
Ans: The isotopes of an element have the same number of electrons in different orbitals. They have the same number of unpaired electrons in the outermost shells. The number of unpaired electrons in the outermost orbitals determines the chemical properties of elements.
Q.14: Define Avogadro’s number? How does it relate to the masses of chemical substances?
Ans: It is the number of atoms, molecules or ions in one gram mole of an element compound and ion. One – gram mole of the substance is the atomic mass, molar mass or ionic mass taken in grams. It means that the number of the species is related with the masses of the species.
Q.15: Prove that one mole of each N₂, CO₂ and H₂ contain equal number of molecules?
Ans: This is according to Avogadro’s law that one mole of a substance has 6.02×10-23 molecules in it. So 28 grains of H2, 44 grams of CO2 and 2 grams of H₂ have 6.02×1023 molecule in each.
Q.16: Differentiate between limiting and non limiting reactants?
Ans: Limiting reactant produces least of products after its complex consumption, while non limiting reactant does not do so.
Q.17: Define Stoichiomety?
Ans: The study of quantitative between the reactants and products in a balanced equation Id called Stoichiometry.
Q.18: Give reasons that one mole of different compounds have different masses but has the same number of molecules?
Ans: One mole of different compound have different masses because different compounds have different molecular masses but all have same number as 1 mole is equal to 6.02×1023 molecules.