Heat Flashcards
What is heat?
the total internal kinetic energy of the particles making up the substance
What is temperature?
the average kinetic energy per particle of the substance indicating how hot or cold it is.
Why does something hot cool down after being in contact with something cold
Heat energy flows from hotter substances to cooler substances until thermal equilibrium is reached. So, the heat from the hot substance is transferred to the cooler substance, reducing the hotter substances temperature which makes it cooler.
What is conduction and identify an example
heat transferal between objects that are in direct contact. heat transferred by faster moving particles colliding with slower particles and they speed up which increases the temp.
heat from stovetop transferring through metal pot of water.
what is radiation and identify an example
Heat is transferred between 2 locations by electromagnetic radiation which is caused by vibrating particles and carries heat away from hot substances. it can be absorbed and cause the particles in a substance to move faster increasing its temp.
eg. the sun
what is convection and identify an example
the flow of heat through a fluid. when a liquid is heated the particles making it move faster and spread out, become less dense, then rise and convection currents are produced.
water in a kettle heating up and moving in currents
Why would plastic be used for a screw-top on a bottle instead of metal.
Plastic is a good insulator, so it doesn’t allow heat to transfer easily.
metal is a good conductor, and it allows heat to transfer earlier, would cause the flask to cool down quicker.
why does a hot drink remain hot for a while in a vacuum flask.
- silvered walls reflect heat back into the flask contents
- vacuum between double walls prevents heat transfer through conduction or radiation. therefore, the contents of the flask remain hotter as there is less heat transferred.
Calculate the heat required to raise the temperature of 0.200kg of water from 25 degrees to 75 degrees.
Q= mc change in temp
= 0.2 x 4200 x 50
= 42000 J
calculate heat required to raise temp of 62 g of aluminium from 15 to 82
q= mc change in t
q= 0.062x 900x (82-15)
=37386
=3.7 x 10 to the power of 4
25 kj of heat energy was added to a 375ml cup of water that was initially a temp of 15. determine final temp
Q= mc change in t
Q=mc (Tf-Ti)
Q=mctf-mcti
q+mcti=mctf
Tf=Q+mcTi/mc
Tf= 25000+0.375 x 4200 x 15/ 0.375 x 4200
= 31 degrees
Copper cube temp of 20 degrees was added to 250 ml of water at a temp of 85. the final temp is 63, determine the mass of the copper.
Change in temp for copper:
63-20
=43 degrees
change in temp for water:
63-85
= -22
Heat gained by cu= heat lost by water
McCcTc= MwCwTw
Mc=MwCwTw/CcTc
Mc=0.25x 4200 x 22/ 390 x 43
= 23100/ 16770
=1.38kg or 1.4kg
What is a specific heat capacity and what does it mean if potatoes have a high heat capacity.
The specific heat capacity of a substance is the amount of heat energy required to raise the temp of 1kg of substance by 1-degree Celsius.
a high specific heat capacity means that potatoes need to lose a large amount of energy to decrease in temperature, so it takes a long time for them to cool down.
if a tub and a sink were both filled with water of the same temperature. Which one has a higher heat?
the tub as it has more mass it has more particles
How does the temperature increase in substances?
heat flows into a material—particles absorb energy from heat flow—-particles vibrate more rapidly—– average kinetic energy of particles increases— temp increases.
