States and Properties of Matter: Notes and PYQs

The correct answer is A, by absorbing radiating heat energy. A change of state is governed by the energy of the particles. When a solid absorbs heat its particles vibrate harder until the force holding them in the lattice is overcome and it melts; further heat lets the liquid particles escape as vapour. Withdrawing heat reverses both steps. Option B is wrong because electrolytes conduct electricity in solution and take part in chemical change; they do not convert a state. Option D is wrong for the same reason, as acids and bases bring about a chemical reaction that gives new substances, not a physical change of state. Option C is the tempting distractor: pressure does matter, and squeezing a gas hard enough liquefies it, but the option is incomplete because raising pressure on a solid or a liquid alone will not change its state and in fact raises the boiling point. Heat is the general agent the question is after.

The correct answer is B, 1924. In 1924 Satyendra Nath Bose sent Albert Einstein a paper deriving Planck s radiation law by counting indistinguishable light quanta. Einstein saw at once that the same statistics applied to atoms, translated the paper into German, had it published and extended it, predicting that a dilute gas of such particles cooled near absolute zero would collapse into a single lowest quantum state. That state is the Bose-Einstein condensate, and the statistics are Bose-Einstein statistics. Option A, 1935, is the year of the Einstein-Podolsky-Rosen paper on quantum entanglement and not of this prediction. Option D, 1919, is the year of the solar eclipse observations that confirmed general relativity. Option C, 1930, has no connection with the condensate. Remember the chain: Bose s statistics and Einstein s prediction in 1924, the first condensate made in the laboratory in 1995, and the Nobel Prize in Physics for it in 2001.

The correct answer is C, P1/P2 = V2/V1 if T is kept constant. Boyle s law applies to a fixed mass of gas at constant temperature and states that pressure is inversely proportional to volume, so the product of the two is a constant: P1 into V1 equals P2 into V2. Rearranging that equality gives exactly the ratio in option C, the first pressure to the second as the second volume is to the first. Option A is the pressure law, often credited to Gay-Lussac: at constant volume the pressure of a gas is directly proportional to its absolute temperature. Option B is Charles s law: at constant pressure the volume is directly proportional to the absolute temperature. Both are true statements of other laws, which is what makes them good distractors here, but neither is Boyle s law. Option D is wrong because option C is a correct statement. Note that the temperatures in A and B must be in kelvin, not degrees Celsius.

The correct answer is B, 4 degrees Celsius. Water contracts as it is cooled from higher temperatures like any other liquid, but only down to 4 degrees Celsius. Below that point the hydrogen bonds begin to lock the molecules into an open, cage-like arrangement and the water expands again. Its density is therefore greatest at 4 degrees Celsius, where one cubic centimetre has a mass of about one gram. This behaviour is called the anomalous expansion of water. Option A, 0 degrees Celsius, is the freezing point, where water has already expanded and ice forms that is about nine per cent less dense, so it floats. Option C, 10 degrees Celsius, is above the point of maximum density, so the water there is slightly less dense. Option D, 100 degrees Celsius, is the boiling point, where water is at its least dense as a liquid. The practical consequence is that a pond freezes from the top down and the bottom stays at 4 degrees Celsius, letting fish survive.

The correct answer is D, plasma. Plasma is a hot, electrically conducting mixture of free electrons and positive ions produced when a gas is heated or strongly ionised. Stars, including the Sun, are made of plasma, and since stars and the ionised gas between them hold the overwhelming bulk of the visible matter in the universe, plasma is the most abundant state. On the Earth it is uncommon and is seen in lightning, the aurora, the flame of an electric arc, neon signs and fluorescent tubes. Option A, solid, is the state of planets, moons and dust, which are a tiny fraction of cosmic matter. Option B, liquid, is rarer still in the universe, since a liquid needs a narrow band of temperature and pressure to exist. Option C, gas, is the usual wrong answer, because interstellar clouds do hold neutral gas, but far more of the universe is ionised than neutral. Plasma is often called the fourth state of matter.

The correct answer is A, bromine. Bromine is a dark reddish-brown, dense, fuming liquid at ordinary room temperature, with a melting point of about minus 7 degrees Celsius and a boiling point of about 59 degrees Celsius. It is the only non-metal that is liquid under these conditions, just as mercury is the only metal that is liquid at room temperature, and the pair is a standard one-mark question. Option B, iodine, is a shining greyish-black solid at room temperature; it is remembered instead as a solid that sublimes readily to a violet vapour. Option C, sulphur, is a brittle yellow solid that melts only near 115 degrees Celsius. Option D, phosphorus, is also a solid at room temperature, white phosphorus being waxy and red phosphorus powdery. Gallium and caesium are sometimes offered as near answers, but both are metals that merely melt a little above room temperature.

The correct answer is B, 80 cal/g, that is about 334 joule per gram. This is the heat one gram of ice at 0 degrees Celsius must absorb to become one gram of water at 0 degrees Celsius; the temperature does not rise at all while it melts, because the energy goes into breaking the hydrogen-bonded lattice. The same amount is given out when water freezes. Option C, 540 cal/g, is the latent heat of vaporisation of water, the heat needed to turn one gram of water at 100 degrees Celsius into steam at the same temperature; candidates routinely swap the two figures, so fix 80 for melting and 540 for boiling. Option A, 22.4, is not a heat value at all but the molar volume of a gas in litre at 0 degrees Celsius and one atmosphere. Option D is simply too large. Because the latent heat of fusion is high, ice is an efficient cooling agent and keeps a drink cold for a long time.

The correct answer is A, the liquid absorbs latent heat from its surroundings. Evaporation is a surface phenomenon in which the fastest-moving molecules of a liquid break free. Doing so needs the latent heat of vaporisation, and that energy is drawn from the liquid left behind and from whatever the liquid touches, so both grow cooler. This is why sweat cools the skin, why water stays cool in an unglazed earthen pot whose pores let water seep out and evaporate, and why a splash of spirit on the hand feels cold. Option B is the reverse process, condensation, which releases latent heat and warms the surroundings. Option C confuses cause with effect: lowering the pressure above a liquid speeds evaporation up, but the cooling itself comes from the latent heat taken away, not from the fall in pressure. Option D is wrong because the cooling does not depend on expansion; a liquid evaporating in the open does not do useful work by expanding.

The correct answer is C, that of the liquid decreases and that of the gas increases. In a liquid the resistance to flow comes mainly from the attraction between neighbouring molecules. Heating gives the molecules energy to slip past one another, so the attraction matters less and the liquid thins; hot honey and warm engine oil pour far more easily than cold. In a gas the molecules are already far apart and attraction is negligible, so viscosity arises from molecules carrying momentum across the flow as they move about. Heating makes them move faster, which transports more momentum, so a gas becomes more viscous. Option A and option B each get one half right and the other half wrong, and option D reverses both. The contrast is the point examiners test, so remember the pair as a single fact: heat thins a liquid and thickens a gas.

The correct answer is B, dry ice is solid carbon dioxide. At ordinary atmospheric pressure carbon dioxide has no liquid stage: the solid passes straight into vapour at about minus 78.5 degrees Celsius. Because it leaves no puddle behind, it is called dry ice and is used to keep ice cream and vaccines cold, to make stage fog and for cloud seeding. Option A, solid nitrogen, is not what the term means; nitrogen is used as a cryogenic liquid at minus 196 degrees Celsius, not as dry ice. Option C, solid ammonia, is wrong as well, although ammonia is a common refrigerant in its liquid form. Option D is the commonest mistake of all: ordinary frozen water, however pure, is just ice, melts into a liquid and is wet. The examinable point is the pair of words: dry because there is no liquid stage, and carbon dioxide because that is the substance that behaves so at atmospheric pressure.

The correct answer is C, inversely proportional to the square root of its molar mass. Thomas Graham found in 1833 that a light gas spreads through a porous partition faster than a heavy one, and that the rates of two gases are in the inverse ratio of the square roots of their densities, and therefore of their molar masses. Hydrogen, the lightest gas, diffuses fastest of all, and since the molar mass of oxygen is sixteen times that of hydrogen, hydrogen diffuses four times as fast. Option A is the opposite of the truth, as a heavier gas is slower. Option B gets the direction right but the power wrong: the dependence is on the square root, not on the mass itself, so it would predict hydrogen to be sixteen times faster than oxygen. Option D contradicts the law altogether. The law explains why the smell of ammonia spreads through a room before that of a heavier vapour released at the same moment.