Latent heat of fusion (solid to liquid change)

Latent heat of fusion (solid to liquid change)

We can study the latent heat of fusion by a simple experiment.

We should first take a beaker and place it on a burner. A thermometer should be suspended in it. The temperature is 0^o C. When we supply heat to the beaker, ice start melting to form water. When temperature is again noted it is still 0. This temperature remains the same time even a little amount of ice is there in the beaker. Till this time all heat provided is used to convert ice in water. This heat is used up in breaking the attractive force between the ice molecules. When no ice is left and only water is there at 0^o C, any additional heat will increase the kinetic energy of molecule thus increasing the temperature, but before that all heat but only help in changing the state of matter.

The latent heat of fusion of a solid is the quantity of heat in joules required to covert 1 kg  solid (at its melting point) to liquid, without any change in temperature.

Latent heat of fusion of ice is 3.34 × 10⁵ J/kg. 1 kg of ice at   0^o C will need 3.34 × 10⁵ J to melt and become ice. When water at 0^o C converts in ice on freezing it gives out 3.34 × 10⁵ J of energy. 

Latent Heat

States of matter

Conversion of states

Latent heat

The heat energy that has to be supplied to a matter to change is state is called latent heat.

Latent does not change the temperature of substance instead this temperature is used up to change the state of matter. Normally, when we supply heat to a substance its temperature increases but when the substance undergoes a change in state this supplied heat is utilized in changing its state.  Literally the word “latent” means hidden or concealed. Latent heat means the hidden heat because it is not visible in form of temperature change by rising the temperature, but this heat is utilized to change the state.

As discussed earlier, every substance solid or liquid has some force of attraction between its particles which hold them together. When the substance changes its state ( from solid to liquid, from liquid to gas) it has to break these attractive forces and so that the particles can move.

Why latent heat only change the state but not the temperature?

Basically, when heat is provided some heat break the attractive force and some heat is utilized in increasing the kinetic energy of particles. Latent heat is used to break the attractive force between particles and not to increase the kinetic energy so the state change but not the temperature.

There are two types of latent heat:

1.      Latent heat of fusion

2.      Latent heat of vaporisation

Latent heat of fusion: It is the heat energy used in converting a substance from solid state to liquid state.

Latent heat of vaporisation: It is the heat energy used in converting a substance from liquid state to gaseous state.

Change in states of matter

Change in states of matter

Matter exists in three different forms: solid, liquid and gaseous state. These forms are interchangeable, i.e. we can change a substance from solid state to liquid state or from liquid state to gaseous state and similarly the reverse from gaseous to liquid state and from liquid to solid state. For example, ice melts to from water and when water is heated it evaporates to form water vapour which is in gaseous state. Likewise when water vapour condenses it forms water and water freeze it converts to ice.

The physical state of matter can be change using two techniques:

1.      Changing the temperature

2.      Changing the pressure

Effect of change of temperature:

The state of matter can be changed by changing the temperature, either by heating or by cooling.

When temperature is increased the kinetic energy of particles increases causing more vibration in particles, this leads to decrease in inter particle attraction. Similarly when temperature is decreased the kinetic energy of particles decreases causing vibration of particles to reduce, this leads to increase in inter particle attraction.

1.      Solid to liquid (Melting):

The process in which a solid substance changes into liquid on heating is called melting. Ice melts to form water.

The temperature at which solid substance melts and changes into liquid form at atmospheric pressure is called the melting point of substance. . Ice melts to form water at 0^o C, so 0^o C is the melting point of ice

Melting point of substance is the measurement force of attraction between the particles of the substance. The greater the force of attraction greater will be the melting point. Melting point of ice is 0^o C and that of wax is 63^o C. this means the intermolecular force of attraction between wax particles is greater than that of ice.

Causes of conversion: when a solid substance is heated, the heat energy make the particles vibrate vigorously. At melting point the solid particles have sufficient kinetic energy to overcome the strong force of attraction which holds the particles of solid in fixed position. This kinetic energy break the particles in smaller units and thus the solid melts to form liquid.

2.       Liquid to gas (boiling or vaporisation):

The process in which a liquid substance changes into gas on heating is called boiling. Water boils to form water vapour.

The temperature at which liquid substance evaporates and changes into gaseous form at atmospheric pressure is called the boiling point of substance. Water evaporates to form water vapour at 100^o C, so 100^o C is the boiling point of water.

Melting point of substance is the measurement force of attraction between the particles of the substance. The greater the force of attraction greater will be the boiling point. Boiling point of water is 100^o C and that of alcohol is 78^o C. this means the intermolecular force of attraction between water particles is greater than that of alcohol.

Causes of conversion: when a liquid substance is heated, the heat energy make the particles vibrate vigorously. At boiling point the particles have sufficient kinetic energy to overcome the strong force of attraction which holds the particles of liquid together. This kinetic energy breaks the particles in individual units and thus the liquid evaporates to form gas.

3.      Liquid to solid (freezing):

The process in which a liquid substance changes into solid on decreasing the temperature is called freezing. Water freezes to form ice.

The temperature at which liquid substance freezes and changes into solid form at atmospheric pressure is called the freezing point of substance. Water freezes to form ice at 0^o C, so 0^o C is the freezing point of water.

Causes of conversion: when a liquid substance is cooled by lowering the temperature, the particles lose energy due to which they start moving slowly. When liquid is cooled enough till its freezing point, its each particle stop moving and vibrate about a fixed point. This is the point when liquid change and become solid.

Diffusion

Diffusion

The spreading and mixing of particles of matter from one substance to another is called diffusion. This diffusion takes place due to the motion of particles from one substance to another.

1.Diffusion is fast in gases whereas in solids it is very slow: diffusion is faster in gases as the particles of gases move more freely, the force of attraction between the molecules are less so they can move independently. In case of liquids the movement of molecules is restricted so they move little slower than gases. In case of solid the intermolecular force is very strong so they rarely move, thus making diffusion very slow in case of solids.

2.Rate of diffusion increases with increase in temperature: when a substance is heated the particles of that substance get kinetic energy so they start moving rapidly making diffusion faster.

Diffusion explained with example:

Diffusion in gases:

1.      Smell of food cooked in kitchen reach us in other room: when food is cooked the gases released from the food contain smell with it. These gas particles containing aroma mix up with the surrounding air and rapidly move ahead to reach us.

2.      Smell of perfume spread due to diffusion.

3.      Smell of warm food can be observed from a distance but to smell the same food when cold we have to get close to it.

Diffusion in liquids:

1.      Crystal of potassium permanganate when placed in water and left undisturbed mixes with each other is due to diffusion. The particles of potassium permanganate spread in water due to diffusion.

2.      A drop of ink spreads in water as the small particles of ink move inside water due to diffusion.

Diffusion in solids:

1.      Two metal blocks when left together close to each other the particles of both diffuse with each other

2.      When blackboard scribbled with chalk is left that way for some time, we cannot clean the board quickly this happens because the particles of chalk diffuse in board and so it gets difficult to remove chalk particles from the board.

Characteristics of particles of matter

Characteristics of particles of matter:

1.      Very small in size.

2.      Have spaces between them

3.      Particles are constantly moving

4.      Particles attract each other

The characteristics of particles can be discussed by experiment.

Particle of matter are very small: we take a beaker full of water and add small amount of ink to it. Ink diffuse in water and spreads uniformly. When more water is added the colour dilutes, this is because few drop of ink is composed of millions of small particles which keep on spreading in large amount of water. 

Particles have space between them: we take a beaker full of water and add small amount of ink to it. Ink spreads uniformly between the spaces present between the particles of water.

Particles are constantly moving: we take a beaker full of water and add small amount of ink to it. Ink spreads uniformly after some time even when we leave it undisturbed, this happens because the particles of matter are constantly moving. The same can be observed with essence sticks, as the gases spread from one corner of room to the whole space.

Particle of matter attract each other: the force of attraction between the particles of same matter is called cohesion. This cohesion is different for different material. Like for liquid and gases they are less but for solid they are large. That is why it is difficult to break apart a solid but it is easier of liquids. We can move our hand through liquid and gases but not through solid. We cannot break iron but ban easily break chalk as cohesive force between the particles of iron is much larger than that of chalk.

  

Matter is made of particles

Every matter is made up of very small particles. These tiny particles are extremely small which cannot be seen even with high power microscope. These small particles that form other objects are called atoms and molecules.

How to prove that matter is made up of small particles.

We can easily observe that matter is composed of small particles by mixing two different things and noticing the two dissolve in each other.

1.      Dissolving solid in liquid

2.      Dissolving liquid in liquid

3.      Mixing two gases

Dissolving solid in liquid: To discuss this we will take

 Potassium permanganate, a purple coloured solid crystalline substance and water, a colourless liquid. When potassium permanganate is added to beaker full of water and leave it as it is, slowly the colour of water will change to purple, this is because the molecules of potassium permanganate separate from one another and diffuse in water. Here diffusion means that the molecules of potassium permanganate spread in water to make a uniform solution.

Dissolving liquid in liquid: To discuss this we will take

 Blue coloured ink and water. When ink is added to beaker full of water and leave it as it is, slowly the colour of water will change to blue, and this is because the molecules of ink diffuse in water. This means that ink and water both are made of small particles.

Mixing two gases: let’s take 2 test tube

One with colourless gas and other with bromine vapour, a red-brown coloured gas when the two test tubes are joined after some time the content of both gases mix with each other. Content of both tubes are made of small particles that diffuse in each other

This diffusion phenomenon gives us two conclusions:

1.      Matter is made of two particles.

2.      These particles have kinetic energy and they are constantly moving.

Matter is made of particles

Matter is made of particles

Every matter is made up of very small particles. These tiny particles are extremely small which cannot be seen even with high power microscope. These small particles that form other objects are called atoms and molecules.

How to prove that matter is made up of small particles.

We can easily observe that matter is composed of small particles by mixing two different things and noticing the two dissolve in each other.

1.      Dissolving solid in liquid

2.      Dissolving liquid in liquid

3.      Mixing two gases

Dissolving solid in liquid: To discuss this we will take

 Potassium permanganate, a purple coloured solid crystalline substance and water, a colourless liquid. When potassium permanganate is added to beaker full of water and leave it as it is, slowly the colour of water will change to purple, this is because the molecules of potassium permanganate separate from one another and diffuse in water. Here diffusion means that the molecules of potassium permanganate spread in water to make a uniform solution.

Dissolving liquid in liquid: To discuss this we will take

 Blue coloured ink and water. When ink is added to beaker full of water and leave it as it is, slowly the colour of water will change to blue, and this is because the molecules of ink diffuse in water. This means that ink and water both are made of small particles.

Mixing two gases: let’s take 2 test tube

One with colourless gas and other with bromine vapour, a red-brown coloured gas when the two test tubes are joined after some time the content of both gases mix with each other. Content of both tubes are made of small particles that diffuse in each other

This diffusion phenomenon gives us two conclusions:

1.      Matter is made of two particles.

2.      These particles have kinetic energy and they are constantly moving.

States of matter

Three states of matter

Now we will discuss the three states of matter : solid, liquid and gas.

Properties of solid:

·         Fixed shape and volume

·         Have high density

·         Do no flow

·         Certain solid can be compressed but not much, eg rubber

Properties of liquid:

·         Have fixed volume but don’t have a ffixed shape

·         They have less density than solid

·         Flow easily

·         Cannot be compressed

Properties of gases:

·         Have no fixed shape or volume

·         Have very low density

·         Flow easily

·         Can be compressed easily

Comparing the properties of solid, liquid and gases

Shape: either it is a book, chair or table every solid have a fixed shape, their shape remains the same wherever we place it. But in case of liquid and gases they do not have a fixed shape because they change their shape according to the container in which they are stored

Volume: solid and liquid have fixed volume, that means that they will occupy a certain required space, a iron ball of volume 100cubic cm when melted and moulded in another shape will still occupy the same space, similarly when 1l of water when kept in a jar or in a tub may change its shape but in both cases it will occupy same 1l of space. In case of gases the gas can be compressed in a small space by applying pressure, LPG and CNG is an example of large amount of gas compressed in small cylinders.

Density: density of solid is maximum, liquid has comparatively less density and gases have even more density. This difference in density is due to gap in molecules of atoms, the atomic gap in case of solid is negligible. They are very closely packed and hence the density is high, the molecules of liquid are comparatively far with each other and gases are even farther so the density of liquid are less and gases even more less.

Flow: the flow of solid is zero, this means that solid cannot flow, this is because they have a defined shape, their molecules are compact without any gap between them, they have high force of attraction among their molecules which keep them from flowing. But in case of liquid and gases they have a defined shape, their molecules are less compact means they are a bit far and the force of attraction between their molecules are less so they can easily flow. Due to these factors gases can flow even more easily when compared to liquids.

Compression: there are a few solids like rubber and sponge that can be compressed under pressure, rubber is elastic in nature so it can change its shape when force is applied, on the other hand sponge has minute pores from which air gets squeezed out when we press it thus changing its shape. Liquid cannot be compressed although it has space between its molecules, gases have lots of space between them so when compressed  they gets squeezed and decrease in volume.

Why salt, elastic and sponge are called solid?

Although when placed in a container salt and sugar take their shape but the single particle of salt have its definite shape which cannot be changed.

Rubber is elastic in nature so it can change its shape when force is applied on it

Sponge has minute pores from which air gets squeezed out when we press it thus changing its shape.

Matter: An introduction

What is matter?

Anything that has volume and mass is called matter. Substance either as light as a feather or as hard as a brick all are matter. Anything which can flow as water or smoke all are matter.

Oxygen and hydrogen are gases, they have volume and mass which is negligible. Water, milk or juice have mass and they occupy space. Sand or brick they have mass as well as they occupy space.

All these are matter.

When we look around us everything that we see is matter. In the morning from using toothbrush till the night while we go in our beds all are matter.

                                                            

On the basis of physical properties matter is classified in three forms: Solid, liquid and gas

Solids are those substance which have fixed shape and volume.

Liquid are those substance which have fixed volume but no fixed shape.

gases are those substance which have no fixed shape and volume.

On the basis of chemical properties matter is classified in three forms: elements, compound and mixtures

Elements : these are the substance in simplest naturally occurring form. These substance cannot be further split in more simpler form using any chemical method.

Elements can be further divided as metal, non-metal and metalloid.

Metal are the strong elements(have high tensile strength) that are good conductor of electricity. They are malleable, ductile and lustrous. They have high density and sonorous.

Non-metal are low tensile strength element that do not conduct electricity. They are brittle and have low melting and boiling point.

Metalloids are the elements that show some properties of metal and some properties of non-metal.

Compounds are substance made up of two or more elements chemically combined in a fixed ratio.

Mixture is a substance that is made up of two or more elements physically combined. mixtures are of two types: homogenous mixture and heterogenous mixtue

Homogenous mixture: this type of mixture have their components uniformly mixed with each other. The components cannot be distinguished.

Heterogeneous mixture: those mixture in which one substance remain separate and can be distinguished from the rest of components are heterogenous mixture.