Water and ChangesWater and Changesof Stateof State

Joe is buying ice kachang …Joe is buying ice kachang …

but when he reached home …but when he reached home …

What happened?What happened?

My ice kachang is all watery and slushy.

Why did this happen?Why did this happen?

steam, water vapour(gas)

water(liquid)

ice(solid)

3 states of water3 states of water

It has definite shape and volume.

It has definite volume but no definite shape.

It has no definite shape and volume.

FreezingFreezing

When you put water into the freezer, water When you put water into the freezer, water loses heat..

At 0At 0ooC, water freezes to C, water freezes to become icebecome ice..

0oC is the freezing point of water.

water loses heat ice

MeltingMelting When ice is just taken When ice is just taken

out of the freezer, the out of the freezer, the temperature of ice is temperature of ice is lower than 0oC..

At 0At 0ooC, ice melts to C, ice melts to become waterbecome water..

0oC is also called the melting point of ice.

It It gains heat from the from the surroundings and its surroundings and its temperature rises to temperature rises to 00ooC.C.

MeltingMelting During the process During the process

of melting, the ice of melting, the ice gains heat but its but its temperature temperature remains at 0oC..

The heat taken in is The heat taken in is used to change the used to change the solid ice to liquid solid ice to liquid water.water.

ice gains heat water

BoilingBoiling When water is When water is

boiled, it boiled, it gains heat..

When the water’s When the water’s temperature reaches temperature reaches 100100ooC, water boils to C, water boils to become steambecome steam..

100oC is called the boiling point of water.

water gains heat steam

water boilswater boilsat 100at 100ooCC

ice meltsice meltsat 0at 0ooCC

water freezeswater freezesat 0at 0ooCC

EvaporationEvaporation Water on the wet clothes Water on the wet clothes

gains heat from the from the surroundings.surroundings.

The water evaporates to The water evaporates to become water vapourbecome water vapour and and escapes into the air.escapes into the air.

water gains heat water vapour

Evaporation occurs all the timeand at any temperature.

FactorsFactorsaffecting the rate of evaporationaffecting the rate of evaporation

temperature

windhumidity

area of exposed surface

The higher the The higher the temperaturetemperaturethe higher the rate of evaporationthe higher the rate of evaporation

The stronger theThe stronger the windwindthe higher the rate of evaporationthe higher the rate of evaporation

The larger theThe larger the area of exposed surfacearea of exposed surfacethe higher the rate of evaporationthe higher the rate of evaporation

The lower the The lower the humidityhumiditythe higher the rate of evaporationthe higher the rate of evaporation

The air in the desert is dry.So Joe’s sweat evaporates quickly.

The air in the jungle is humid. So Sue’s sweat evaporates slowly.

CondensationCondensation The cool surface of the The cool surface of the

glass cools the air glass cools the air surrounding it.surrounding it.

The water vapour in the air The water vapour in the air loses heat and condenses and condenses (to (to become waterbecome water) on the ) on the surface of the glass.surface of the glass.

Condensation can take place at any temperature.

water vapour loses heat water

CondensationCondensationat higher temperaturesat higher temperatures

As steam As steam loses heatloses heat, it , it condenses to condenses to become become waterwater..

The white “clouds” (that The white “clouds” (that you see) are tiny water you see) are tiny water droplets.droplets.

cloudsclouds

steam loses heat water

Losing heatLosing heat

freezing

condensationgas(steam, water vapour)

liquid(water)

solid(ice)

Gaining heatGaining heat

liquid(water)

solid(ice)

gas(steam, water vapour)

melting

evaporation /boiling

What happens What happens when other things when other things

gain heat?gain heat?

Candles are made from wax.Candles are made from wax.Wax melts when it gains heat.Wax melts when it gains heat.

candles

Butter melts when it gains heat.Butter melts when it gains heat.

butter

The alcohol on these swabs The alcohol on these swabs evaporates easily when it gains heat.evaporates easily when it gains heat.

alcohol

Perfumes are liquids that evaporate Perfumes are liquids that evaporate easily when they gain heat.easily when they gain heat.

perfumes

liquid(water)

solid(ice)

3 states of water3 states of water

steam, water vapour(gas)

At a glance …At a glance …Water freezes into ice at 0Water freezes into ice at 0OOC. This is C. This is

called the called the freezing pointfreezing point of water. of water.

Ice melts into water at 0Ice melts into water at 0OOC. This is C. This is called the called the melting pointmelting point of water. of water.

Water boils and produces steam at Water boils and produces steam at 100100OOC. This is called the C. This is called the boiling pointboiling point of water.of water.

At a glance …At a glance …

Water evaporates into water Water evaporates into water vapour at any temperature.vapour at any temperature.

Steam or water vapour condenses Steam or water vapour condenses to become water.to become water.