Changes in States

Changes in States

Freezing….Boiling….

Sublimation….

Condensation……Evaporation

Freezing

To explain the movement of particles in the process of _____________.

Freezing

 (a)   Freezing : ___________ state __________

state.

liquid solid

freezing

Liquid particles Solid particles

Explanation using KPT When a liquid is cooled, the temperature ________

until its freezing point is reached.

During freezing, the liquid particles will lose the

heat energy to the surroundings as they

____________ to take up ________

and________ positions in the solid.

Note: For all pure substances, the freezing point is the same as the melting point.

drops

Slows down fixed

orderly

Reading a Graph on Freezing

temperature remains constant

freezing completes

freezing starts

freezing point (=melting point)

SOLID

LIQUID + SOLID

LIQUID

temperature (ºC)

time from start (min)

Reading a graph on freezing Graph shows how temperature of substance changes with time

during

melting when it is heated steadily.

1. PQ - the substance is completely ______________.

2. Point Q - ____________ begins at _________.

( The ______ drop of liquid begins to form a ______).

3. QR - ________ continues to take place. The substance

exists as a ________ of _____ and __________.

4. Point R – The last drop of _________ will change into a ______

5. RS – The substance is completely __________

liquid

solid690C

first

freezing

freezingmixture liquidsolid

liquid solidsolid

Think……..

Why does the temperature remain constant between QR even though the substance is continuously cooled?

Ans:

During cooling heat is given out by particles as they take up fixed positions is equal to heat loss from the surround during cooling.

Sublimation It is a process where a _________ when heated changes

directly into a ________ without going through a _________ state.

During sublimation, heat energy is _________ to _______________________.

Examples of substance that sublimes:

1. Dry ice

2. Iodine (crystals to purple vapour)

3. Moth balls

4. Ammonium chloride, NH4Cl

solid

forces of attraction absorbed

liquidgas

Condensation

It is a process where a _________ is changed into a ______ or _______.

During condensation, heat energy is _________ to form back the _________________________.

Gas

liquid solid

forces of attractiongiven out

Evaporation

It is a process where a _______ is changed into a ______ but it occurs _____ the boiling point of the liquid.

During evaporation, heat energy is ___________ to ____________________________.

liquid

absorbed

gasbelow

break the forces of attraction

Differences between evaporation and boiling

Evaporation Boiling

1. Occurs at the surface of liquid

1. Occurs in the whole liquid

2. Occurs over a range of temperature

2. Occur at fixed temperature e,g water boils at 100 degree celsius

3. No bubbles are formed 3. Bubbles are formed within

the liquid

Some liquids whose boiling points are not far from the room temperature tends to evaporate easily. Such liquid are called _________ liquids. E.g nail polish remover ; perfumesvolatile

Summary Melting ; Heat energy is _______

_____________ ; Heat energy is _______

(2)

(5)

(3)(4)

Predicting states

Example:

What would be the state of substance X

at room temperature given the mp is 400C

and bp is 1090C.

Ans: Everyone look on board!