Thermal Properties of Matter

Water has maximum density at 4°C. When a lake freezes from the top, the ice layer insulates the water beneath. The water at the bottom remains at approximately 4°C because this is the temperature at which water is densest and sinks. The water below the ice doesn't reach 0°C or below because the ice acts as an insulator.

Pure water reaches its maximum density at approximately 4°C. At this temperature, 1 gram of water occupies exactly 1 cubic centimeter of volume. This is why water is densest at 4°C - below this temperature, the molecules start forming an open crystal structure (approaching ice).

Heat required to melt 10g ice at 0°C = 10 × 80 = 800 cal. Heat available from 10g water cooling from 10°C to 0°C = 10 × 1 × 10 = 100 cal. Since only 100 cal is available, only 1.25g of ice can melt (100/80). The remaining 8.75g ice stays at 0°C, so final temperature is 0°C with some ice still present.

At 0.6% alcohol in blood, one gets the feeling of relaxation and warmth.

This is the correct answer. Ocean thermal plants can operate only when the temperature difference between water at the surface and water at the depths up to 2 km is more than 293 K or 20^o C, which is required to boil liquid ammonia and the vapours run the turbine.

Boiling water for 15 - 20 minutes kills the harmful germs in it.

Correct answer. Elevation in boiling point (ΔT_b) = K_b x iNaCl x mNaCl = (0.51^oC kg mol^-1) x (2) x (0.25 mol/kg) = 0.26^oC The boiling point of 0.25 molal NaCl = 100.00^oC + 0.26^oC = 100.26^oC

Correct answer. 100.0 g of 45% mix: 45.0 g C₂H₂(OH)₂ + 55.0 g H₂O nglycol = 45.0 g / 62.0 g mol^-1 = 0.73 mol mglycol = (0.73 mol / 0.055 kg) = 13.272 mol Kg^-1 ΔT_f = (1.86^oC kg mol^-1) x (13.272 mol Kg^-1) = 24.7^oC Freezing point = 0.00°C – 24.7°C = -24.7^oC

Correct answer. Assume that we use 1 L of ethylene glycol and 3 L of water. The mass of ethylene glycol will be 1.11 kg and that of water will be 3.0 kg. So, the total mass of the solution is 4.11 kg. Number of moles of ethylene glycol = 1110 g / 62 g mol^-1 = 17.9 mol Molality of ethylene glycol = 17.9 mol / 4.11 Kg = 4.36 mol Kg^-1 Freezing point depression ΔT_f = K_f x molality of solution For water, K_f = 1.86 K kg⁻¹ mol ΔT_f= (1.86 K kg⁻¹ mol) x (4.36 mol Kg^-1) = 8.1 K

The melting point of ice is 0°C, which is also the freezing point of water. At this temperature, ice and liquid water can coexist in equilibrium. 273°C is far above water's boiling point, and negative values would represent temperatures below freezing, not melting.

0^oC = 273 K 6^oC = 273 K + 6 K = 279 K

It is the boiling point of water on Kelvin scale. 

We know that 4.2 Joules of heat energy is required to raise the temperature of 1 gram of water by 1⁰C. So, heat energy required to raise the temperature of 100 grams of water by 3⁰C is 1260 Joules (100 X4.2 X3 = 1260)

Seawater has a freezing point of about − 1.8°C (28.8°F).

Water boils when it reaches its boiling point of 100ºC. This is the temperature at which water turns to steam or water vapour. Steam is an invisible gas. At this temperature, water evaporates very fast.