We boil water for cooking or to make it potable almost every day of our lives. But what exactly is on the boil? Boiling is the process of heating a liquid sample to the point where all of the liquid is converted to vapour.
The boiling point is at this temperature. The temperature at which air pressure equals the vapour pressure of a liquid is known as the boiling point of that material.
At 1 atm, the usual boiling point of water is 99.97°C, while at 1 bar, the standard boiling point is 99.61°C.
Boiling is a large-scale phenomena in which all molecules (not just those on the surface) are involved.
This article will explain if boiling water is a chemical or physical change, as well as the differences and qualities of the two types of changes.
We’ll also look at the factors that influence boiling point and the distinction between boiling and evaporation.
Is it true that heating water causes a chemical change? Boiling water does not change the chemical composition of the water, hence it is not a chemical change. During the boiling of water, just the physical state of water changes from liquid to water vapour. Boiling produces water vapours with the same molecular structure as liquid water, i.e. H2O.
For more information, look at the subheadings below.
Why does boiling water not cause a chemical reaction?
This question can only be answered if we understand what happens throughout the boiling process.
Heat must be supplied from an external source in order for water to boil. When you heat water, the temperature rises at first.
Water molecules’ kinetic energy rises, and they clash with one another. When the temperature reaches the boiling point of water, all of the water molecules cease to be liquid.
The heat delivered at the boiling point causes the water molecules to alter their physical state, while the temperature remains constant.
Even if heat is continuously delivered, the temperature remains constant during boiling because heat is a type of energy, and liquid water requires some energy called enthalpy of vapourization to change state from liquid to vapour.
There is no chemical reaction that occurs during the boiling process. There is no formation of a new compound. The modification is also reversible.
These features lead us to believe that boiling water is not a chemical change.
Is a Physical Change Caused by Boiling Water?
Boiling water is, in fact, a physical transformation.
This is due to the fact that the chemical composition of water does not change during the boiling process.
In addition, the procedure is reversible. By simply chilling the vapours, liquid water can be recovered.
Changes in Physical and Chemical Properties
A change occurs whenever a reaction occurs in chemistry. Reactants are transformed into products.
There are two types of changes: physical and chemical.
Below is a summary of the differences between the two.
|Basis||Physical Change||Chemical Change|
|Definition||During the reaction, only physical properties are changed, and chemical properties remain unchanged.||During the reaction, along with physical properties, chemical properties are also unchanged.|
|Reversibility||They are mostly reversible and therefore are temporary changes.||They are mostly irreversible, and therefore these are permanent changes.|
|Product||No new substance is formed as a product. The chemical composition of the product is the same as the reactant.||One or more substances that have different chemical compositions are formed as a product.|
|Example||Boiling of water, tearing of paper, etc.||Boiling of egg, curdling of milk, etc.|
What are the differences between physical and chemical properties?
Physical qualities are those that can be measured without changing a substance’s chemical composition.
For example, a substance’s size can be determined without affecting its chemical composition.
Physical attributes are also divided into two categories: intensive and extensive.
Extensive properties are those in which the value of a property changes as the mass of the substance changes, whereas intensive properties are those in which the value of a property does not vary as the mass of the substance changes. Bulk properties are intensive properties.
The volume of a substance, for example, changes as its mass changes.
As a result, it is a large property. The temperature, on the other hand, does not change as the mass changes, and it is an intense feature.
Chemical attributes are those that can’t be measured without affecting a substance’s chemical composition.
The reactions of a compound with oxygen, water, acid, base, or any other chemical are examined in general. They investigate whether the substance is capable of undergoing a chemical reaction.
For example, only if the product created has a different composition can we analyse the reaction of hydrogen with a material.
If the composition remains the same, no chemical reaction occurs.
Water Phase Diagram
A system’s phase is a homogenous and unique state. There is no obvious line dividing the phase into sections.
For example, solid ice is one phase, but there are two phases when some of it melts and remains in equilibrium with water.
A phase diagram can be used to show the different physical states of a substance at different temperatures and pressures.
A phase diagram is a graphical representation with the y-axis representing pressure and the x-axis representing temperature.
• A phase diagram is split into three sections. There is only one phase in each place.
Only ice can be found between the y-axis and the ODB.
Only water vapour is present between the x-axis and the ODC.
Only liquid water is present in the EDB area.
• The lines are in a state of balance with two phases.
Solid and vapour equilibria are represented by OD.
Solid and liquid equilibria are represented by DB.
Liquid and vapour equilibria are represented by DC.
• All three phases coexist at the point of intersection of three lines (D), and this temperature and pressure is referred to as the triple point.
• The line depicting solid and liquid equilibrium has a negative slope. This means that as pressure rises, the melting point drops.
This is also the reason why ice has a lower density than liquid water.
• The line indicating liquid and vapour equilibrium has a positive slope. This means that as pressure rises, the boiling point rises as well.
This could also explain why the volume of vapour is greater than that of liquid.
Transitioning from one phase to the next when boiling water
There is a change in the phase of water from liquid to vapour during the boiling process.
The equilibrium can be illustrated by line DC when all of the liquid has not turned to vapour at the boiling point. The energy for phase shift comes from the external heat.
The volume of a liquid increases dramatically when it turns into a vapour.
At atmospheric pressure, a sample liquid (phase=1) is heated. The air pressure is assumed to be constant. The temperature of the sample rises as it is heated.
When the temperature reaches the boiling point, the liquid phase begins to convert to vapour, and the two phases are in balance (liquid and vapor).
On continuous heating, all of the liquid is turned to vapour, and there is just one phase.
Boiling Point Influencing Factors
A substance’s boiling point is not a universal constant. It may be changed by altering circumstances such as air pressure and liquid vapour pressure.
The normal boiling point is the temperature at which water boils under atmospheric pressure of 1 atm.
The new boiling point is lower than the usual boiling point if the external pressure is less than 1 atm.
The new boiling point is higher than the usual boiling point if the external pressure is more than 1 atm.
The higher the air pressure, the more energy the liquid need to boil, and so the boiling point is higher when atmospheric pressure is high.
The vapour pressure is affected by the external temperature, which in turn affects the boiling point.
When a non-volatile solute is introduced to the liquid under investigation, the boiling point rises. The vapour pressure is affected by the solute.
Because of their chemical composition and intermolecular interactions, different substances have varying boiling points. The boiling point rises as the intermolecular forces become stronger.
Evaporation and Boiling
Both processes undergo a state shift, yet they are vastly different.
Evaporation of the Evaporation of the Evaporation of the Evaporation of the E
|Definition||It is the process by which vaporization of liquids takes place at a particular temperature called as boiling point||It is the process in which the vaporization of liquids takes place at room temperature.|
|Temperature Change||The temperature remains constant during boiling.||Evaporation is accompanied by a decrease in temperature.|
|Condition||A liquid boils only when the external pressure is equal to the vapor pressure.||Evaporation takes place only when the air is not saturated with water vapor. (Clothes do not dry quickly in humid weather)|
|Type of phenomenon||It is a bulk phenomenon||It is a surface phenomenon|
|Application||Boiling water produces steam which is used in cooking||Drying clothes|
- Pressure cookers are designed for use in mountainous environments. The height is higher in mountainous areas, and the atmospheric pressure is lower.
Because of these conditions, water has a low boiling point and is turned to vapours before the meal is cooked.
As a result, pressure cookers are employed to raise the boiling point.
They raise the water’s external pressure, resulting in greater boiling points and well-cooked food.
People in the plains often use pressure cookers to speed up the cooking process.
- As previously stated, non-volatile solutes raise the boiling point of a liquid.
As a result, adding salt to water raises the boiling point of the water and makes cooking easier.
Boiling water does not result in a chemical change since the chemical characteristics of water do not change. Boiling only affects the physical qualities of the substance. Boiling does not result in the formation of a new product.
Good luck with your studies!