Introduction
Physical properties
· Melting point
· Boiling point
· Vapor pressure
· Heat capacity
Melting point
The melting point is the temperature at which a substance changes from a solid to a liquid is called the melting point.The melting point of a substance is the temperature at which it changes state from solid to liquid.
At the melting point, the
solid and liquid phases exist in equilibrium. The melting point of a substance
depends on pressure and is usually specified at a standard pressure such as 1
atmosphere or 100 kpa. It is difficult, though, to find a melting point,
usually, chemists can only obtain a melting range of a 2-3C accuracy. This is
usually sufficient for most uses of the melting point.
The temperature of the reverse change from a liquid to a solid is referred to as the freezing point or crystallization point. Because of the ability of some substances to supercool, the freezing point is not considered a characteristic property of a substance.
Melting point range
Span of temperatures from the point at which the crystals first are liquefied to the point at which the entire sample is liquid.
* Pure compounds usually melt over a narrow temperature range of
1-2C.
*Presence of soluble impurity almost always decreases and broadens
the melting point range.
Examples of melting point
*The melting point of ice is 0C. The melting point of a solid is the same as the freezing point of the liquid. At that temperature, the solid and liquid states of the substance are in equilibrium. For water, this equilibrium occurs at 0C.
Properties of melting point
The following are melting point properties.
*Color is intensive
*Density is intensive
*Mass is extensive
*Volume is extensive
*Melting points are extensive. The Temperature at which a
substance melt.
Factors affecting melting point
*Ionic bonds
*Intermolecular forces
*Shapes of molecules
*Size of molecules
Boiling point
The boiling is the temperature at which a substance changes from a liquid to a gas. The boiling point of a liquid is the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure of the liquid's environment. At this temperature, the liquid is converted into a vapour.
The boiling point of the liquid depends upon the pressure of the surrounding. If a liquid is at high pressure, it has a higher boiling point. The normal boiling point or atmospheric boiling point of a liquid is the special case in which the vapour pressure of the liquid equals the defined atmospheric pressure at sea level one atmosphere.
Boiling points examples
Examples of boiling points in our everyday life.
*Vapour pressure and boiling.
*Atmospheric pressure and boiling.
*Boiling point Elevation.
*Boiling point and water.
Boiling point properties
The boiling point is the temperature at which the vapour pressure
of a chemical equals atmospheric pressure. Simply put, it measures the
temperature at which a chemical boil. Same to melting point a higher boiling
point indicates greater intermolecular forces and therefore less vapour
pressure.
How does boiling point occur?
When atoms or molecules or liquid can spread out enough to change from a liquid phase to a gaseous phase bubbles form and boiling occurs. The boiling point is the temperature at which boiling occurs for a specific liquid. For example, the boiling point is 100C at a pressure of 1atm. The boiling point depends on temperature, atmospheric pressure, and vapour pressure.
When a liquid boil, what is inside the bubbles
The bubbles in a boiling liquid are made up of molecules of the
liquid which have gained enough energy to change to the gaseous phase.
The boiling point of milk
The boiling point of milk is about 212F, so it is never actually brought to a boil during the pasteurization process.
Factors affecting the boiling point
Pressure: the biggest determinant of a liquid's boiling point is
the surrounding pressure.
Intermolecular bonds: when we consider other liquids more factors
help to determine the boiling point.
Solutes, solvents, and solutions.
How intermolecular forces affect the boiling point
The higher the intermolecular forces between the liquid particles,
the harder it is for it to escape into the vapour phase, I.e., you need more
energy to convert it from liquid to the vapour phase and the higher its boiling
point.
Vapor pressure
Vapor pressure or equilibrium vapour pressure is defined as the
pressure exerted by a vapour in thermodynamic equilibrium with its condensed phase
(solid or liquid) at a given temperature in a closed system. The equilibrium
vapour pressure is an indication of a liquid's evaporation rate. It relates to
the tendency of particles to escape from the liquid or a solid. A substance
with a high vapour pressure at normal temperature is often referred to as
volatile.
The pressure exhibited by vapour present above a liquid surface is
known as vapour pressure. As the temperature of liquid increases the kinetic
energy of its molecules also increases. As the kinetic energy of molecules
increases, the number of molecules transitioning into a vapour also increases.
thereby increasing the vapour pressure.
Vapor pressure is nothing but the tendency of particles to escape from the liquid or a solid. At normal temperatures substance with a high vapour pressure is often referred to volatile. With the increase in the temperature, the vapour pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapour bubbles.
Lowering of vapour pressure
Lowering of vapour pressure is defined as the difference between vapour pressures of pure solvent and the vapour pressure of solvent from solution is called lowering of vapour pressure.
Examples of vapour pressure
Humid Air: one of the best examples of vapour pressure in real
life is the relative humidity experienced by a person in a particular area.
*Smell of brandy or whiskey.
*LPG cylinders.
*Pressure cooker.
* Boiling of liquids.
*Water present in lakes
*Skin cracks
*Frost formation in freezers
Characteristics of vapour pressure
Vapor pressure depends on temperature and nothing else. The
vapour pressure of a liquid does not depend on the amount of the liquid in the
container, be it one liter or thirty liters, at the same temperature, both
samples will have the same vapour pressure.
Vapor pressure has an exponential relationship with temperature and always increase as temperature increase. When a liquid is boiling its vapour pressure is equal to the external pressure. For example: as the water boils at sea level, its vapour pressure is 1atmosphere because the external pressure is also 1atmosphere.
Applications of vapour pressure
Vapor pressure, related to the boiling point and heat of vaporization, is the most important characteristic in the application of fats to fried food preparation. Triglycerides have extremely low vapour pressures, so evaporation does not occur.
Vapour pressure of a liquid
* The vapour pressure of a liquid is the point at which
equilibrium pressure is reached in a close container between molecules Leaving
the liquid and going into the gaseous phase and molecules Leaving the gaseous
phase and entering the liquid phase.
Vapour pressure increases or decreases
* As the temperature of a liquid or a solid increase its vapour
pressure also increases.
* Conversely vapour pressure decreases as the temperature
decreases.
* The vapour pressure of a liquid can be measured in a variety of
ways.
Highest vapour pressure
Ether has the highest vapour pressure at any temperature. The reason for its high vapour pressure is that the attractions are less between ether molecules than between water and alcohol molecules.
Lowest vapour pressure
Mercury exerts the lower vapour pressure because of the strong
bond among its atoms.
Heat capacity
Heat capacity or thermal capacity is a physical property of matter defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin. Heat capacity is an extensive property. The corresponding intensive property is the specific heat capacity found by dividing the heat capacity of an object by its mass.
Dividing the heat capacity by the amount of substance in moles yields its molar heat capacity. The volumetric heat capacity measures the heat capacity per volume. In architecture and civil engineering, the heat capacity of a building is often referred to as its thermal mass.
Heating on a molecular level
* When an object is heated its molecules will observe the heat
energy.
* This heat energy is converted to kinetic energy.
* Enabling the molecules to move faster.
* Wilt the increase in the speed of the molecules, we would see
the temperature rise of the substance.
Specific heat capacity
* Specific heat capacity is defined as the amount of energy needed
to raise the temperature of 1kg of the substance by 1C or 1k.
Heat capacity types
There are two types of heat
capacity.
* Heat capacity at constant volume
* Heat capacity at constant pressure
* The heat supplied to a system to raise its
the temperature through 1C keeping the volume of the system
constant is called heat capacity at constant volume.
Examples of heat capacity
* When we heat a pot of water on the stove, the pot heats up
faster we are putting the same amount of heat on both substances the pot
responds quicker than the water because water has a high heat capacity.
Characteristics of heat capacity
* It has no shape, no mass, no color, no odor, no volume, and no
weight. It is an invisible form of energy.
* The presence of warmth is left only through its effect on
matter. It might be transferred from one body to another
High heat capacity
* Heat capacity is related to the substance's ability to retain
heat and the rate at which it will heat up or cool. For example, a substance
with a low heat capacity such as an iron will heat and cool quickly while a
substance with a high heat capacity, such as water, heats and cool slowly.
Types of heat capacity
* Specific heat capacity, thermal expansion, heat conduction,
thermal radiation and thermoelectric force are all aspects of thermal
performance.
Heat capacity used
* Heat capacity or specific heat capacity is the amount of heat
per unit mass required to raise the temperature.
* Specific heat is useful in determining the processing the
temperature and amount of heat necessary for processing and can be useful in
differentiating between two polymeric composites.
Causes heat capacity
* The capability of a molecule to absorb heat energy is called
heat capacity. Waters' high heat capacity is a property caused by hydrogen
bonding among water molecules.
* When heat is absorbed hydrogen bonds are broken and water
molecules can move freely.
Lowest heat capacity
* Gold is a heavy metal that has a very low heat capacity. Radon
also has a very high molecular weight and heat capacity. These of highest and
lowest of all elements.
Water heat capacity
* The exact value of the specific heat capacity of water is 4182
J/kgc. Now water is quite commonly occurring and a vital substance in our life
therefore there is a special way to identify the total amount of heat energy
needed to raise one gram of water by a calorie.
Heat capacity increase with temperature
* Many properties of substances vary with temperature, and so does
heat capacity. On a deeper level as we raise the temperature and more degrees
of freedom and unfreeze, so the heat capacity grows.
Solid heat capacity
* For a monoatomic substance where there is no motion
corresponding to the rotation of atoms around each other the heat capacity of
the liquid is only very slightly higher than that of the solid.
Molar heat capacity of solid
* Molar heat capacity or specific heat capacity is the amount of
heat energy required to raise the temperature of 1mole of a substance. In the
SI unit molar heat capacity is the amount of heat in joules required to raise 1
mole of a substance 1 kelvin.
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