The graph above shows the heating curve of water. One can plot heating curves by

Question

The graph above shows the heating curve of water. One can plot heating curves by measuring the increase in temperature of a given amount of ice, water or steam as a function of heat that is added at a constant rate. The first slope (from A to B) refers to the change in temperature of ice as heat is added. At the melting point of ice (B) the temperature remains constant until all of the ice is melted. The graph between C and D represents the increase in the temperature of water, until the boiling point is reached (D). At the boiling point the temperature of the water remains constant until all of the water is converted into steam (from D to E). The last portion of the curve (from E) represents the heating of steam.

Determine if the following statements are True or False.

Select all that are True:
1.Water in the gaseous phase does not exhibit any hydrogen bonds between water molecules.
2.Heating steam is an exothermic process which decreases the internal energy of the system.
3.Condensation is an exothermic process because the system gives off energy.
4.The water in the system is undergoing a reversible process at 273K and 1 atm pressure. Under these conditions, both melting and freezing may occur.
5.When water freezes (from C to B), hydrogen bonds are formed between water molecules.
6.The melting of ice is an endothermic process because the system absorbs energy.
7.Hydrogen bonds between water molecules are broken when evaporation occurs. (From D to E)
8.The freezing of water is an exothermic process because the system gives off energy.

Explanation / Answer

1.Water in the gaseous phase does not exhibit any hydrogen bonds between water molecules. True

In gaseous phase H2O molecules are far apart so they cannot have intermermolecular bonds.

2.Heating steam is an exothermic process which decreases the internal energy of the system. False

Energy absorbed by the steam so it is a endothermic.

3.Condensation is an exothermic process because the system gives off energy. True

Condensaton is bond making process so energy is given off: exothermic

4.The water in the system is undergoing a reversible process at 273K and 1 atm pressure. Under these conditions, both melting and freezing may occur. True

Because at 273 K, water and ice are at equilibrium

5.When water freezes (from C to B), hydrogen bonds are formed between water molecules. True

More number of Hydrogen bonds are formed when water freezes

6.The melting of ice is an endothermic process because the system absorbs energy. True

absorption of energy is a endothermic process.(ice melts by absorbing energy)

7.Hydrogen bonds between water molecules are broken when evaporation occurs. (From D to E) :True

water evaporates by breaking hydrogen bonds.

8.The freezing of water is an exothermic process because the system gives off energy. True

Water freezing means making strong bonds or making more bonds between water molecules

So while making bonds energy is released.

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