Inter-conversion of states Done by: Leon Ng Joo Keat of 1O2 (20) Science Ace Term 2

Aims: To find out the differences between evaporation and boiling. To find out how do these phenomenal occur. To find out why melting point and freezing point occur at the same temperature. To find out how does evaporation occur and how can it occur on the surface. To find out how does boiling occur and how can it occur in the water.

Definition What is evaporation? It is the process of a liquid converting to the gaseous state. What is boiling? It is the process of a liquid converting to the gaseous state by heating to its boiling point.

How does evaporation occur? When the molecules escape from the body of the liquid and move freely away, as a gas. Some molecules have high enough energy to escape from the surface of the liquid. Molecules of higher-than-average kinetic energy escape from the liquid, leaving it cooler than it was before they escaped. Example: clothes become dry, wet floors become dry etc.

Factors that influenced the speed of evaporation The surrounding temperature The wind speed The surface of water exposed to the air The air humidity The colour of the object

How does boiling occur? The spontaneous change of water from the liquid phase to the gas phase. The vapour pressure of a liquid is equal to the atmospheric pressure on the liquid. Liquid particles are freed and change into gas. Sufficient heat energy enables the particles to overcome and break the forces of attraction between the particles Examples: water boils etc.

1)Differences (evaporation)  Evaporation occurs on the surface of liquid  Evaporation occurs at every temperature below the boiling point of the liquid  Evaporation takes a longer time for the liquid to “disappear” completely  The speed of evaporation is slow

2)Differences (boiling) Boiling occurs at the bottom of the liquid Boiling occurs only at the boiling point of the liquid Boiling takes a shorter time for the liquid to “disappear” completely The speed of boiling is quick

Boiling point What is boiling point?  The temperature at which the vapour pressure of the liquid equals to the environmental pressure.  The temperature at which the surface of the boiling liquid is agitated and bubbling.  The temperature when a liquid begins to boil and becomes a gas or vapour.

Conclusion 1)Evaporation occurs on the surface of the liquid while boiling occurs at the bottom of the liquid. 2)Evaporation occurs at every temperature below the boiling point of the liquid while boiling occurs solely at the boiling point of the liquid.

3)Evaporation takes a longer time for the liquid to “disappear” completely compared to the time taken for the liquid to “disappear” completely during the boiling process. 4)The speed of evaporation is slower while the speed of boiling is faster.

But Why? Why do these happen? What makes them like this? How do these happen?

1)Why does evaporation occurs on the surface of the liquid while boiling occurs in the liquid? When we boil a liquid, we heat from the bottom of the liquid. As a result, large bubbles of water vapour form at the bottom and rise to the surface. If we applied the same heat to the surface of the water, it would evaporate just as quickly but we would not call it boiling as bubbles would not form and rise to the surface. Evaporation occurs on the surface of the water as the surface of the water contacts with the heat in the air and when it gathers enough heat, it evaporates. This is mainly due to the movement of the liquid particles which occurs at every temperature.

The boiling point is the temperature when the liquid particles are freed and changed into gas. The particles are only able to overcome and break the forces of attraction between particles at boiling point when the heat energy is sufficient. Evaporation occurs at every temperature as long as kinetic energy is produced among the particles and particles at the surface can overcome attractive forces and escape to form a gas. 2) Why does evaporation occurs at every temperature below the boiling point of the liquid while boiling occurs solely at the boiling point of the liquid?

Melting point and freezing point What is melting point? the temperature at which the solid melts to become a liquid What is freezing point? the temperature at which the liquid turns into solid

Melting point and freezing point  Melting point and freezing point of a water is 0 degree Celcius.  Melting point and freezing point will vary according to the impurity of the liquid.  A liquid will remain at its melting point until it has completely melted into a liquid and the temperature increases only after that  Different liquids have different melting point and freezing point

Why are the melting point and freezing point of a liquid are at the same temperature? The melting point and freezing point are normally the same as the a liquid freezes and melts as the same temperature. The temperature it freezes is the freezing point and the temperature it melts is the melting point which are the same. For instance, the water freezes and melts at 0 degree Celcius. This does not include “supercooled” situation when the liquid is cooled to temperatures below the freezing point without forming into a solid.

What is the difference between the melting point and the freezing point of a liquid? The melting point and freezing point of a liquid are the same as the only difference is the direction from which the phase change is approached. For example, ice melts into water when you warm it up to 0 degree Celcius while water solidifies when you cool it down to 0 degree Celcius.

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Thank you! Any questions? Do not hesitate to ask.