When a substance alters from one state, or phase, of matter to an additional we say that it has actually undergonea change of state, or we say the it has actually undergone a readjust of phase. Because that example, ice melts and becomes water; water evaporates and becomes water vapor.

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These alters of phase constantly occur v a change of heat. Heat, i m sorry is energy, either comesinto the material during a readjust of phase or warm comes out of the material during this change. However, althoughthe heat content that the material changes, the temperature go not.

Here space the five alters of phase. They room diagrammed in the opening animation and listed below.

Description of phase ChangeTerm for Phase ChangeHeat Movement during Phase ChangeTemperature change During phase Change
Solid to liquidMeltingHeat goes into the solid together it melts.None
Liquid to solidFreezingHeat leaves the liquid together it freezes.None
Liquid come gasVaporization, which has boiling and also evaporationHeat goes right into the liquid as it vaporizes.None
Gas come liquidCondensationHeat pipeline the gas together it condenses.None
Solid to gasSublimationHeat goes into the solid together it sublimates.None

So, how can there be a readjust in heat during a state adjust without a change in temperature?During a readjust in state the heat energy is offered to adjust the bondingbetween the molecules. In the case of melting, added energy is supplied to breakthe bonds in between the molecules. In the situation of freezing, power issubtracted as the molecules bond come one another. These power exchanges space not alters in kinetic energy.They are transforms in bonding energy between the molecules.

If warmth is coming into a substance during a phase change, then this energy is supplied to rest thebonds in between the molecule of the substance. The instance we will use right here is ice cream melting right into water.Immediately ~ themolecular bond in the ice are broken the molecule are relocating (vibrating) at the sameaverage rate as before, therefore their mean kinetic power remains the same, and, thus, their Kelvin temperatureremains the same.

Below is a photo of solid ice cream melting into liquid water. The molecule of ice and also the molecule of water (the blackballs) are moving with the same rate of vibration in this diagram. This ismeant to show that they have the same mean speed and thus the sameaverage kinetic power (since they have the same mass) and also thus the sameKelvin temperature. The movements are, though, significantly exaggerated. Actually,the activities of the molecules must be thought about tiny vibrations.


At the minute of melt the typical kinetic energy of the molecule does no change.The warm is supplied to rest the bonds between the ice molecules together they turn into a fluid phase.Since the average kinetic energy of the molecules does not readjust at the minute of melting, the temperature of the molecule does no change.Since both the ice and the water molecules have the same average kinetic power at the moment of melting, the temperature of both space the same.

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// change of statevar loopWait = 50; // ms.var iceXO; // initial x-coordinatevar iceYO; // initial y-coordinatevar iceX; // existing x-coordinatevar iceY; // existing y-coordinatevar waterXO;var waterYO;var waterX;var waterY;// molecule vibrationvar amplitude; // amplitude, both moleculesvar fx; // x-frequency, both moleculesvar fy; // y-frequency, both molecule var phase; // phase balance out for water moleculevar t; // existing timevar dt; // delta timevar twoPi = 2 * Math.PI;setup = function()// initial position for ice moleculeiceXO = 140;iceYO = 120;// initial position for water moleculewaterXO = 170;waterYO = 195;fx = 2; // x-frequency because that both moleculesfy = 3; // y-frequency because that both moleculesamplitude = 10; // amplitude the vibration because that both moleculesphase = 1; // step of vibration for water moleculet = 0; // current timedt = .1; // delta time;loop = function()// find new positions for moleculesupdate();// attract molecules at new positionsrender();// wait a bit, execute it againloopTimeout = setTimeout(loop, loopWait);;update = function()// this math moves the molecule in a Lissajous figure// calculate molecule positions at the existing timeiceX = Math.floor(iceXO + amplitude * Math.sin(fx * t));iceY = Math.floor(iceYO + amplitude * Math.sin(fy * t));// phase change water molecule vibration// the movements are identical, other than one lags behind the otherwaterX = Math.floor(waterXO + amplitude * Math.sin(fx * t + phase));waterY = Math.floor(waterYO + amplitude * Math.sin(fy * t + phase));t += dt; // tic the clock to the following time for the next update// store the time between 0 and also two times pi// because two time pi is the natural period of the sine functionif(t > twoPi) t -= twoPi;;render = function()// place DOM imagesiceImg.css("left", iceX.toString() + "px");iceImg.css("top", iceY.toString() + "px");waterImg.css("left", waterX.toString() + "px");waterImg.css("top", waterY.toString() + "px");;

In the ice cream the molecules room strongly external inspection to oneanother, thus creating a strictly solid. When warmth is included to the ice these bonds are broken and the ice cream melts. The molecules climate bondto one an additional with less strength and a different geometry, and also water is formed.

Now, prior to the melting, the molecules were actually relocating when in the hard state. Castle werevibrating back and forth. They had actually an mean kinetic energy. So they had actually a Kelvintemperature proportional come this mean kinetic energy.

After the melt the water molecules are still vibrating. And they have the same average kinetic power as lock had prior to the melting. So, the water is in ~ the exact same temperature at the minute after the melting the the ice cream was in ~ the moment prior to the melting.

Heat came into the situation, yet it to be not offered tochange the kinetic power of the molecules. It was offered to readjust thebonding in between the molecules. Breaking the bonds between the molecule ofthe ice needs energy, and this energy is the added heat.

In a similar method heat beginning a liquid to readjust the molecular bonding as soon as the liquid boils orevaporates into a gas, and also heat enters a hard to adjust the molecular bonding as soon as it sublimates into a gas.

In one inverse method heat pipeline a gas to change the molecular bonding when the gas condenses intoa liquid, and also heat pipeline a liquid to adjust the molecular bonding once it freezes into a solid.

In no one of these alters of state is the warm (energy)that is input or output used to change the rate of the molecules. The typical speed of the molecules is the exact same before and after a step change, and also so is the average kinetic energy.

Heat (energy) is transferred into the ice.The warmth is offered to break the bonds between molecules, not to rise the typical kinetic power of the molecules.Since the bonds amongst the ice molecules have been broken, water is formed. The water molecules, in ~ this moment, have the same mean kinetic power as castle did as soon as they to be ice.

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Since the ice and water molecule both have actually the same typical kinetic energy, they space at the same Kelvin temperature.

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