P1a Flashcards
(21 cards)
What does the rate of cooling depend on for warm materials?
The temperature difference compared to the surroundings. The greater the difference in temperature, the faster the rate of cooling will be. For example, a hot cup of coffee will cool down quicker in a cold room than in a warm room.
What are the consequences of the direction of energy flow between materials of different temperatures?
Energy tends to flow from hot objects to cooler ones. For example, warm radiators heat the cold air in your room because heat flows.
What is temperature a measurement of?
Of hotness/ a measure of the average kinetic energy of the particles in a substance. The hotter something is, the higher its temperature, and the higher the average KE of its particles.
What are the scales for temperature?
Arbitrary/ chosen scale.
What is temperature represented by?
Colour in a thermogram.
What do the different colours represent in a thermogram?
The hottest parts are white, yellow and red and the coldest parts are black, purple and dark blue.
What is heat a measurement of?
Energy. When a substance is heated, its particles gain KE. This energy makes the particles in a gas or a liquid move around faster. In a solid, the particles vibrate more rapidly. This is what eventually causes solids to melt and liquids to boil.
What is the scale heat is measured on?
An absolute scale, meaning it can’t go lower than zero , because there’s a limit to how slow particles can move.
What does the energy needed to change the temperature of a material depend on?
Mass, the material from which it is made, and the temperature change. For example you need 4200J to warm 1kg of water by 1oC, but only 139J to warm 1kg of mercury by 1oC.
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees celcius. The measure of how much energy a substance can store is called its specific heat capacity.
Which materials can store a lot of heat?
Materials which need to gain lots of energy to warm up also release loads of energy when they cool down again.
What is the specific heat capacity of water?
High at 4200J/kg/oC. Once water’s heated. it stores a lot of energy, which makes it good for central heating systems. Also, water’s a liquid so it can easily be pumped around a building.
What is the equation for specific heat capacity?
Energy(J) = Mass(kg) x SHC(J/kg/oC) x temp change (oC)
What may be required when using the equation?
Changing the units, such as from g to kg, and finding an initial calculation of temperature change.
What happens when you heat a liquid?
The heat energy makes the particles move faster. Eventually, when enough of the particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid - this is boiling.
What happens when you heat a solid?
Heat energy makes the particles vibrate faster until eventually the forces between them are overcome and the particles start to move around - this is melting.
Why does the temperature not change during a change of state?
When a substance is melting or boiling, you’re still putting in energy, but the energy’s used for breaking intermolecular bonds rather than raising the temperature - there are flat spots on the heating graph. When a substance is condensing or freezing, bonds are forming between particles, which releases energy. This means the temperature doesn’t go down until all the substance has turned into a liquid, condensing, or a solid, freezing.
What is specific latent heat?
The energy needed to change state. The SLH of melting is the amount of energy needed to melt 1kg of material without changing its temperature (i.e. the material’s got to be at its melting temperature already). The SLH of boiling is the energy needed to boil 1kg of material without changing its temperature (i.e. the material’s got to be at its boiling temperature already).
What is specific latent heat different for?
Different materials, and for boiling and melting.
What is the equation for specific latent heat?
Energy (j) = mass (kg) x SLH (J/kg)
What may be required when using the SLH equation?
A change in units or subject so you may be finding the mass instead of energy.
