Chemistry · Solutions · NEET
When a gas dissolves in water, it releases heat. This makes it an exothermic process. By Le Chatelier's principle, if you add more heat (make the water hot), the system tries to remove that extra heat, so the gas comes back out. So heating pushes gas OUT and cooling pulls gas IN. This is opposite to most solids like sugar, which usually dissolve MORE in hot water. NEET loves to test this difference.
It DECREASES with a rise in temperature. Cold water can hold more dissolved gas; hot water holds less. NCERT says the amount of gas dissolved (Henry's law) 'decreases with increase of temperature.' Remember the direction clearly: temperature UP, gas solubility DOWN.
Soda is CO2 gas dissolved in water under pressure. When the drink is warm, the gas is much less soluble, so the CO2 escapes quickly and the drink loses its fizz (goes flat). A cold soda keeps its gas longer because cold water holds gas better. This is a common NCERT example you can use to remember the rule.
In COLD water. Fish breathe oxygen (O2) that is dissolved in the water. Cold water holds more dissolved oxygen, so fish get enough to breathe. Hot water holds less O2, so it is harder for fish to survive. This exact statement appeared in NEET 2026 and was marked CORRECT.
Henry's law says gas solubility depends on the pressure of the gas above the liquid (more pressure = more gas dissolved). Temperature is a separate factor. The Henry's law constant KH itself changes with temperature: hotter water gives a larger KH, which means lower solubility. So higher temperature lowers solubility, and higher pressure raises it. Keep the two factors separate: PRESSURE up = more dissolved; TEMPERATURE up = less dissolved.
A gas molecule is free and moving fast. When it enters water, it slows down and gets held by weak attractions to water molecules. Forming these attractions releases energy as heat, so the overall dissolving of a gas gives out heat (exothermic). Because heat is a 'product', adding heat (hot water) shifts the balance backward and the gas leaves the water.
Identify the correct statements: (A) Molality of 2.5 g of ethanoic acid (M = 60 g/mol) in 75 g of benzene is 0.556 m. (B) Molarity of 5 g NaOH (M = 40 g/mol) in 450 mL solution is 0.278 M. (C) Aquatic species are more comfortable in cold water. (D) The solubility of a gas increases with decrease in pressure. (E) For a binary mixture of A and B, mole fraction of B is x_B = n_A/(n_A + n_B).
Assertion (A): Helium is used to dilute oxygen in diving apparatus. Reason (R): Helium has high solubility in O2. Choose the correct answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes, for almost all common gases like O2, N2 and CO2, solubility drops as temperature rises. Dissolving these gases is exothermic, so heat drives them out.
For most solids, dissolving absorbs heat (endothermic), so heating helps them dissolve. For gases, dissolving releases heat (exothermic), so heating pushes them out. Opposite behaviour.
KH increases as temperature rises. Since solubility is inversely related to KH (p = KH·x), a bigger KH means lower gas solubility in hot water.
Yes. It appears as direct statements (like NEET 2026 'aquatic species prefer cold water') and inside Henry's law and thermal-pollution questions. It is easy marks if you remember the direction: temperature up, gas solubility down.
When hot water from factories is dumped into rivers, the warm water holds less dissolved oxygen. This lowers O2 for fish and can harm aquatic life. It is a real-life example of gases being less soluble in hot water.
