Thermodynamics

The reaction shows a decrease in the number of gaseous moles: 3 moles of gases react to give 2 moles of gas and 1 solid. Since solids have much lower entropy than gases, the overall entropy decreases.

At 100°C, raising the pressure causes the gaseous H O to condense into liquid water.

The total heat is the sum of the heat required to raise the temperature of ice, melt it, raise the temperature of water, and then vaporise it.

The second law of thermodynamics allows for local decreases in entropy, as long as the total entropy of the system (including the surroundings) increases. The breakdown of nutrients in his body contributes to this increase.

Since NaCl dissolves spontaneously in water, the heat of hydration must be negative, indicating an exothermic process. The magnitude of the heat of hydration is greater than 786.

Reaction potential does not change when the reaction is reversed, while enthalpy, Gibbs energy, and rate constants do.

For an isothermal and reversible compression, the work done on the system can be calculated using the formula: Here, mole, cal/mol·K, K, and the volume ratio .
Substituting these values:

The change in entropy when heat is transferred between two reservoirs at different temperatures is given by: Here, , , and .
Substituting these values: Thus, the total change in entropy is 10 J/K, as it involves both the transfer of heat from the hot reservoir to the cold and the temperature difference.
Thus, the correct answer is (d).

A hot air balloon rises because the hot air inside the balloon is less dense than the cooler air outside. According to Archimedes' principle, an object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the object. In the case of a hot air balloon, the hot air inside the balloon is less dense than the surrounding cooler air, so it displaces a larger mass of cooler air, resulting in an upward buoyant force. This force is greater than the weight of the balloon, causing it to rise.

Hence, the correct answer is (d).

Beyond the critical point of H2O, the substance enters a supercritical state, where liquid and gas phases merge and the substance is no longer a typical molecule of H2O. It exists as a superheated fluid without distinct liquid and gas phases. Thus, the correct answer is (d).

The heat of combustion of ethanol is given by the formula: Where: - is the mass of ethanol in grams - is the energy released in joules - The standard heat of combustion for ethanol is Thus, option (d) is the correct answer.

Since the temperature drops during the reaction, it indicates that the system absorbs heat from the surroundings. This type of reaction is called endothermic, as heat is absorbed rather than released. In an endothermic reaction, the enthalpy change ( ) is positive because the system's internal energy increases due to the absorption of heat.

Therefore, is positive, indicating that the reaction is endothermic.

- Statement I is true because the heat capacity of a substance is defined as the amount of heat required to raise the temperature of the substance by one degree Celsius (or one Kelvin). It is an extensive property and depends on the quantity of the substance.

- Statement II is false because specific heat depends not only on the substance but also on its phase (solid, liquid, or gas). For example, the specific heat of water in its liquid form is different from its specific heat when it is in the solid state (ice) or in the gas state (steam). Therefore, the phase of the substance must be considered when discussing specific heat.

- Statement III is true because when a substance undergoes expansion, the heat is spread over a larger volume, which leads to a smaller increase in temperature. This occurs because the energy required to increase the temperature is distributed over a greater number of particles or volume.

Therefore, the correct answer is (c) I and III.