14. a. Why can not a chemical change be normally reversed?
b. Why is it always essential to balance a chemical equation?
c. What happens when Co, gas is passed through lime water and why does it
disappear on passing excess CO?
d. Can rusting of iron take place in distilled water?
Answers
Answer:
a)Because chemical changes produce new substances, they often cannot be undone. For example, you can't change ashes from burning logs back into wood. Some chemical changes can be reversed, but only by other chemical changes.
b) According to the law of conservation of mass ,the number or mass of reactants should be equal to number or mass of products. So the chemical equation should be balanced
c) When CO2 gas is passed through lime water the solution turns milky white and becomes turbid . When excess gas is passed the solution becomes colourless.
d) Distilled water can readily absorb oxygen from the atmosphere when compared to normal tap water (since tap water will already have dissolved impurities in it). This will as a result help in rusting. So yes, rusting of iron can take place in distilled water, provided it is not a closed system.
Answer:
(a) In a chemical change, the products are quite different from the reactants. Therefore, it cannot be normally reversed.
(b) A chemical equation has to be balanced to meer the requirement of the law of conservation of mass. According to the law, the total mass of the reacting species taking part in the reaction is the same as that of the products formed. Since there is a direct relationship between the mass of the different species and their number, it is always essential to balance a chemical equation.
(c) Because they differ in the arrangement of carbon atoms present and have different shapes. The attractive forces among the atoms in the two cases are not same. That is why they evolve different amount of heat.
C(diamond)+O2(g)→CO2(g)+393⋅5kj ltBrgt C(graphite)+O2(g)→CO2(g)+395⋅4kj
Please note that diamond and graphite are the two allotropic forms of carbon. For details, consult chapter 4.
(d) No, rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen not carbon dioxide. Both are essential for the rusting of iron.
Explanation: