OCT/NOV 2002
1. CH4 + 2O2 --> CO2 + 2H2O and 2C2H6 + 7O2 -> 4CO2 + 6H2O
Basically, 10 cm3 of CH4 forms 10 cm3 of CO2 (we're talking of gases); 10 cm3 of C2H6 makes 20 cm3 of CO2 (note the equation above represents 20 cm3 of C2H6). Potassium Hydroxide is an alkali and would absorb CO2 due to acid-base neutralization. Hence the total gas volume = the gas absorbed by alkali = 20 + 10 = 30 cm3.
7. Covalent lattices involve large amounts of covalent bonds. Ice has discrete water molecules; iodine is also present as diatomic molecules; tin(IV)chloride IS a giant lattice but not covalent (metal + non-metal usually forms an ionic compound). Silicon(IV)oxide is of course, a giant molecule with covalent bonds.
10. Option A is stupid because conversion of heat energy into chemical energy is basically the principle of every reaction--it has nothing to do with it being endothermic. Similarly, option B is just as stupid because an exothermic reaction can equally have a high or low activation energy. Option C states the obvious; any species which forms a new molecule would obviously form a new bond, regardless of whether it is exothermic or endothermic. To support Option C we must know whether bond-breaking of NO requires less energy than released in the bond-making processes. Option D has stated an actual reason--if products have high enthalpy change of formation, there is a greater likelihood that they will release more energy than required for breaking bonds of NO and CH4, resulting in an exothermic reaction.
16. Once in an ionic solution, most ions are dispersed and several compounds may be formed due to their insolubility as soon as they form an interaction. Think of a crowd of people in the mall. Whenever a couple enters the mall, they are forced apart by the huge crowd and the woman might end up holding some unknown man's hands. If the form a bond which is unbreakable (e.g. precipitation, where the products are insoluble), they will be a new couple and will leave the mall together. However, if they cannot form a bond (the salt is soluble in water), they will keep breaking away and holding new hands (the salt will be there and yet, will continue forming attractions to other anions/cations). Only CaCO3 is insoluble and hence is obtained.
17. High electronegativity of Cl2 could indicate high reactivity, stronger bond with H and low activation energy. But this is NOT a confirmatory analysis--reactivity is decided basically on bond strength than anything else, and electronegativity alone predict bond strength or activation energy. Hence, do not rely on this option. For Option B, remember that activation energy can be just as likely high and low for exothermic or endothermic reactions, hence we cannot use this as a clue. Option D is false. Option C, the correct option, declares that HI has a smaller bond energy than HCl; it is not only true but it gives a valid clue because a compound at a lower energy is more stable. A product of endothermic reaction is always less stable than the reactants and an unstable compound has a low bond energy. We know that I2 is more stable than Cl2, hence HI will be almost most definitely less stable than I2 and vice versa.
31. Methanal is HCHO, Ethanoic Acid is CH3COOH while Methyl Methanoate is HCOOCH3. All will give an empirical formula as CH2O, hence all are correct and answer is A.
39. View it like this; ethanol is almost neutral, with slightly--slightly acidic inclinations while sulphuric acid is basically a very strong acid. I think (I'm not sure) that viewing their relative strengths, H2SO4 is going to act as a strong acid (proton donor) and hence the CH3CH2O(+)H2 and HSO4- will be formed.
