Heat and Changes of State

Heat and Changes of State

Recap of the previous concepts

• Melting is changing from solid to liquid, for example: ice to liquid water.

• Freezing is the changing of a liquid into a solid.

• Freezing point is the temperature at wich melting occurs.

• Freezing point deppresion is when you lower the freezing point by the addition of soultes like salt. This happens because the solute molecules get in the way of the liquid molecules and make it more difficult to come together and cohere, more energy must be removed for the liquid to freeze.; thus, the freezing point is decreased.

• Cohesion is the attraction between the molecules of the same substance.

Recap of the previous concepts

• Latent heat is the "hidden" heat absorbed or released when a substance undergoes a change of state. The temperature does not rise because all of the thermal energy absorbed is used to loosen the cohesion between molecules.

• Heat of fusion is the latent heat required to change a given mass of a solid into a liquid without changing its temperature.

• Evaporation or vaporization is the change of a substance from a liquid into a gas.

• Volatile liquids are liquids that evaporate rapidly compared with water. For example: nail polish remover

• Nonvolatile are liquids that evaporate slowly compared with water.

Multiple Choice

Heat of fusion is referred as the heat that takes lowering the freezing point of a substance?

• True

• False

Multiple Choice

Evaporation is the process that takes heat and changes a substance from liquid to solid

• True

• False

Multiple Choice

Melting is the energy required to change from phase to phase without increasing temperature

• True

• False

Multiple Choice

Heat of fusion is the latent heat required to change a given mass of a solid into a liquid without changing its temperature

• True

• False

Multiple Choice

Freezing point is the temperature at wich a liquid changes into a solid

• True

• False

Boiling

• When evaporation occurs throughout a liquid, the liquid has begun to boil.

• The temperature at wich a substance boils is its boiling point.

• Boiling is an unnatural process where the liquid gets heated up and vaporized due to continuous heating of the liquid.

• Bubbling effect is not visible in natural evaporation; you can see the bubbling effect in the process of boiling.

Multiple Choice

When evaporation occurs throughout the liquid, the liquid has begun to boil.

• True

• False

Boiling and pressure

Water boils at 100°C at sea level because that is the temperature at which its molecules have enough energy to overcome both their own cohesion and the atmospheric pressure of 101.3 kPa upon them.

If the atmospheric pressure is reduced, the molecules can overcome cohesion easily and boil at less temperature than 100°C

Multiple Choice

The boiling point of a liquid can increase if you increase the pressure at wich the liquid is found.

• True

• False

Boiling point elevation

• The addition of solutes changes the boiling point of a liquid. Nonvolatile solutes raise the boiling temperature, a phenomenon called boiling point elevation. For example, the boiling point of water can be raised by the addition of salt.

• The salt particles make it more difficult to escape from the liquid, it takes more energy to bring the water to a boil, thereby increasing the boiling point.

Multiple Choice

You can DECREASE the boiling point of a liquid by adding salt.

• True

• False

Multiple Choice

The addition of solutes changes the boiling point of a liquid.

• True

• False

Heat of vaporization

The quantity of heat required to change a liquid ALREADY at its boiling point into a gas without raising its temperature is another form of latent heat, called heat of vaporization.

Multiple Choice

Heat of fusion is the latent heat necessary to change a liquid into a gas.

• True

• False

Multiple Choice

Latent heat is the heat absorbed or released when a substance undergoes a change of state without changing its temperature.

• True

• False