Why does the temperature of a substance remains constant during a change of state?

Answer 1

When you add heat to ice at zero degrees celsius the energy causes the movement of ice molecules to increase. When the ice molecules get enough energy, their movement causes them to break free of one another and change to a liquid form. When more heat is added the water molecules absorb that energy and move faster, causing an energy and move faster, causing an increase in temperature (an increase in average energy). When the water molecules absorb enough energy (at about a hundred degrees celsius) they are able to change state again froma liquid to a gas (steam).

Answer 2

For a change of state to occur, heat or energy must be supplied, you'll notice when heating a substance, say ethanol which vapourizes at about 298K, that a vapour is forming and the temp. should remain constant, this is because the entire solution must absorb sufficient energy so that it all vapourizes, only at this point can the solution resume a climb in temperature.

Answer 3

As we know that temperature is changed only when kinetic energy of the substance is changed. When substance is changing its state, the kinetic energy of the substance is being used up by the substance. Hence there is no change in temperature.

Answer 4

During a change of state an amount of energy (termed the latent heat of vapourization for liquid to gas or latent heat of fusion for solid to liquid, and vice versa) is used to reorganize the chemical structure of the molecule. This energy can therfore not be used to increase or decrease the temperature of the substance. Intramolecular an intermolecular bonds must be broken and reformed.

Google "Cooling Curves" to get a basic understanding of this idea. I have not done this myself, but have studied them extensively.

Answer 5

Yes the temperature remains constant. For example: In the ice the molecules are strongly bonded to one another, thus forming a rigid solid. When heat is added to the ice it melts, and these bonds are broken, The molecules afterward bond to one another with less strength, and water is formed.

Now, before the melting, the molecules were actually moving when in the solid state. They were vibrating back and forth. They had an average kinetic energy. So they had a Kelvin temperature proportional to this average kinetic energy.

After the melting the water molecules are moving, also. And they have the same average kinetic energy as they had before the melting. So, the water is at the same temperature the moment after the melting that the ice was at the moment before the melting.

Heat came into the situation, but it was not used to change the kinetic energy of the molecules. It was used to change the bonding between the molecules. Breaking the bonds between the molecules of the ice requires energy, and this energy is the added heat.

Answer 6

During a change of state, such as melting or boiling, the energy being absorbed or released is used to change the arrangement of the particles rather than increase their kinetic energy, which is what determines temperature. This results in the temperature remaining constant until the change of state is complete.

Answer 7

assertion invalid, temperatures of substances can change in a reaction.

Answer 8

Because energy is being used to overcome intermolecular forces.