Anomalous Expansion of Water

Anomalous Expansion of Water

• Water behaves differently from most liquids (and solids and gases) when heated or cooled

• Water typically expands when heated and contracts when cooled, it is an exception to this rule

• Water behaves normally for the most part, expanding when heated and contracting when cooled, it starts behaving abnormally between 0°C and 4°C

• Water contracts when heated and expands when cooled within the temperature range of 0°C to 4°C

• This unique behavior explains why ice occupies more space than water

• Water contracts as it cools from room temperature (25°C) to 4°C

• Water starts to expand once the temperature drops below 4°C

• The expansion continues until the water freezes into ice at 0°C, resulting in ice having a greater volume than water

Consequences of Anomalous Expansion of Water:

• The maximum density of water occurs at 4°C, the only temperature at which both cooling and heating expands water
• The anomalous behavior explains why ice floats on water, as ice has more volume than water and is less dense

Application of Anomalous Expansion of Water:

• The anomalous behavior of water is essential for aquatic life
• Water under the ice stays liquid when a pond freezes over in winter due to this unique property
• Water expands instead of contracting as the temperature decreases from 4°C to 0°C
• The warmer, denser water settles at the bottom, while the cooler, less dense water floats at the top
• Ice, being the least dense, forms the top layer of the pond
• Ice acts as an insulating blanket, keeping the water below warm and allowing underwater life to thrive during winters due to its poor heat conductivity.

Difference Between Heat Energy and Temperature

• Heat energy is the total amount of thermal energy possessed by an object, including kinetic and potential energy

• Temperature is the degree of hotness or coldness of an object

• Temperature is the average kinetic energy of an object

• Heat energy is measured in Joules

• Temperature is measured in Kelvin (S.I unit), Celsius, and Fahrenheit

• A calorimeter is used to measure the amount of heat energy.

• A thermometer is used to measure temperature.

• Temperature and heat are interrelated

• Higher levels of heat energy mean higher temperature while lower levels of heat energy mean lower temperature.

Thermometer Working Principle

• Liquid-in-glass thermometers, including laboratory and clinical thermometers, are commonly used

• They are filled with either mercury or alcohol

• Celsius to Kelvin conversions: C = K - 273; K = C + 273

• Thermometers work on the principle of using heat-sensitive materials that show a visible change with varying temperature

• Materials that display a property that changes uniformly with temperature are used in thermometers

• "Uniformly" means the behavior is consistent for increasing and decreasing temperature.

Considerations for Thermometric Material

• Gold would not be a good choice for a thermometric material

• Gold does not display consistent behavior when temperature changes

• A thermometric scale is a way to measure temperature quantitatively

• The Celsius scale is the most commonly used temperature scale

Mercury as a Thermometric Liquid

• Advantages: good conductor of heat, allowing the liquid to quickly reach the temperature of the surroundings
• Disadvantages: poisonous, fairly low expansivity, and expensive
• It is expensive and also needs to be placed in places that won't freeze as it has a high freezing point of -29°C.

Alcohol as a Thermometric Liquid

• Advantages: expands uniformly, responds quickly to temperature changes, has a visible meniscus, relatively high boiling point (78°C), and is cheap
• Disadvantages: wets the tube, low freezing point (-115°C), large expansivity, and needs to be dyed since it is colorless and doesn't react quickly to temperature changes

Transmission of Heat Energy

• Heat is a form of energy that is transferred from a region of higher temperature to one of lower temperature
• Heat transfer continues until both regions reach the same temperature
• Heat is transferred by conduction, convection, and radiation

Conduction

• Conduction is the transfer of heat through a material from hot to cold regions without any visible movement or flow of the material
• In solids, atoms or molecules vibrate constantly about their fixed positions
• When one part of a solid gets hot, the atoms gain energy and vibrate more strongly, colliding with neighboring particles.

Convection

• Convection involves the transfer of heat from one part of a fluid to another through the movement of the fluid itself
• When part of a fluid is heated, it expands, becomes less dense, and rises, with cooler fluid sinking to take its place
• The circulating stream of fluid creates a convection current that carries heat rapidly
• Convection currents are formed due to changes in densities caused by heating

Radiation

• Radiation does not require any medium for the transfer of heat energy
• The heat from the sun reaches earth through radiation
• Heat travels in the form of electromagnetic waves, emitted in all directions at the speed of light during radiation
• With emission/radiation, heat energy moves from hot objects to the surroundings in the form of radiation.
• With absorption, heat energy moves from the surroundings and is released into surrounding hot objects in the form of radiation.
• The rate at which an object radiates or absorbs heat by radiation depends on its temperature and the nature of its surface
• Hotter objects radiate more heat

Factors Determining Rate of Radiation

• The rate at which an object radiates or absorbs heat via radiation depends on its temperature and the nature of its surface
• The hotter the object, the more it radiates

Practical Applications

• The vacuum between the glass walls prevents heat transfer by convection and conduction since both processes require a medium

• The shiny, silvered and smooth glass walls reduce heat transfer by radiation

• The stopper, made from poor heat conductors like cork or plastic, minimizes heat transfer by conduction and convection

• Heat is a form of energy that is transferred from a region of higher temperature to one of lower temperature.

• A cold object will absorb heat from warmer surroundings, while a warm object will lose heat to cooler surroundings.

Everyday Applications of Conduction

• Conduction happens whenever heat is transferred quickly through a substance

• Good conductors like metals are made into cooking utensils, electric irons, kettles, boilers, toasters, and soldering irons

• Air is a good insulator of heat

• Trapped air acts as an insulator, used in materials like fur, feathers, wool, sawdust, double-glazed windows, fibreglass, expanded polystyrene, cotton wool, and cork.

• This insulation reduces the loss or gain of heat by conduction

Applications of Convection in Buildings and Nature

• Convection currents help in maintaining ventilation in homes and buildings

• Heat emitted from our bodies warms the surrounding air, causing it to rise and escape through ventilation holes

• Fresh, cooler air enters through windows or other openings near the floor

• Land heats up faster than the sea during the day

• Warm air over the land expands, becomes less dense, and rises

• Cool air from the sea moves in to replace the rising warm air, creating a sea breeze

• The land loses heat faster than the sea at night

• Now air comes in, because the cooler air is more dense

• Cool air then moves to fill its place. The effect is air from land is pulled over the sea the whole time

• During the day the warm heated air from the land goes to the sea and the cold dense air comes from their

• At night the pattern reverses. The cooler air that has cooled from the land goes to the sea and the warmed air stays there

Convection in air-conditioners

• Because heat is now being pumped away and warm air keeps coming away, because it is less dense, then as that effect happens continues to occur and distributes heat

• Movement of heater water rises, becomes less dense and cooler, denser water from above enters to take its place

• Convection is formed by elements such as this heater, this effect ensures even heating through the effect, forming a system of water heating

• Water heats at the base and then there is distribution

• An object can increase its absorption of heat energy from its surroundings by having a dull, black and rough surface.

• Fuel storage tanks use shiny, silvery and smooth surfaces to reflect radiation and keep their contents cool

• The shiny, silvery and smooth surface reduces heat absorption from its surroundings by reflecting the heat.