Thermal Properties Of Matter Flashcards
What is internal energy?
Sum of KE and PE of atoms in body.
Define ‘Random thermal energy’.
Total kinetic energy molecules have in a body.
What happens to the internal energy of body as temperature increases?
Internal energy increases.
What is heat capacity C?
Amount of thermal energy required to raise temperature of object by 1 degree or 1K.
What is specific heat capacity?
Amount of thermal energy required to raise temperature of 1kg of material by 1 degree or 1K.
Why does water have a high specific capacity?
Able to absorb a lot of heat before its temperature rises by 1 degree.
What is an example of water being a good cooling agent?
Radiator of car engine.
What is an example of water being a good heating agent?
Hot water bottle able to keep patient warm.
What are some materials with low specific heat capacities?
Metals like copper and steel.
Why do metals have low specific heat capacities?
Very little energy required to heat up cooking utensils.
What happens when a solid melts?
- Heat absorbed, but temperature of substances remains unchanged.
- Heat absorbed known as latent heat of fusion.
What happens during freezing?
- Liquid changes into solid.
2. Latent heat of fusion released, temperature remains unchanged.
Why does the temperatures of ice remains constant when it melts?
- When ice melts, thermal energy supplied(LHOF) causes internal energy of water molecules to increase.
- Since temp constant at 0, KE remains unchanged.
- PE changed due to change in separation between molecules.
What are the factors affecting melting point of water?
- Addition of impurities like ice. Lowers MP of water to below 0.
- Increase in pressure reduces MP of ice.
What happens when liquid boils?
- Thermal energy transferred to liquid without temp change.
- Latent heat of vaporization absorbed by liquid to change to vapor at its BP.
What happened during condensation?
Vapor changes into liquid at constant temp.
What are some factors affecting BP of water?
- BP of water increase when salt added.
- BP increase above 100 when external pressure increase.
- Water boils below 100 when pressure above water decreases.
What are some applications of boiling water under reduced pressure?
- Refining of cane sugar at low pressure saves fuel costs.
2. Evaporated milk produced by boiling milk under reduced pressure at low temp so vitamins not destroyed by heat.
What happens during evaporation?
- Liquid molecules that have KE escape from liquid surface.
- Molecules remaining in liquid have lower KE.
- Hence temp of liquid lowers.
What is an example of evaporation producing a cooling effect?
- Hand rubbed with ethanol feels cool because ethanol evaporates rapidly.
- Heat required for evaporation is absorbed by hand.
Give an example of application of cooling by evaporation.
- When seating occurs, heat absorbed by body.
2. This cools down body.
What are the factors affecting rate of evaporation?
- Surface area
- Temperature
- Humidity
- Wind
How does surface area affect rate of evaporation?
- Bigger surface area
- More molecules on surface
- More molecules able to escape.
How does temperature affect rate of evaporation?
- Higher temp = higher KE.
2. More molecules able to escape.
How does humidity affect rate of evaporation?
- High humidity = higher amt water vapor in air(above liquid).
- Liquid molecules that escape can collide with water molecules in air and return back.
How does wind affect rate of evaporation?
- When there is breeze.
- Breeze blow away water molecules that evaporate.
- When space above liquid surface is clear of vapor, subsequent liquid molecules that escape from liquid will not be knocked back into liquid.
What are the differences between boiling and evaporation?
- B at fixed temperature. E at ALL temp below BP.
- B take place throughout whole liquid, E only at liquid surface.
- B faster rate, E slower rate.
- B causes bubbles, E no bubbles.
What is latent heat L of a substance?
Thermal energy transferred when substances changes from one state to another at constant temp.
What is specific latent heat l?
Thermal energy transferred when unit mass of substances changes from one state to another at constant temp.
