P1 notes

Heat and Temperature

heat is a measure of energy

• when a substance is heated, its particles gain kinetic energy
• this energy makes the particles in a gas or a liquid move around faster
• in a solid, the particles vibrate more rapidly
• this energy is measured on an absolute scale (this means it can't go lower than zero, because there's a limit to how slow particles can move)
• the unit of heat energy is the joule

temperature is a measure of hotness

• temperature is 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
• temperature is not measured on an absolute scale

energy flows from hot to cold

• energy tends to flow from hot objects to cooler ones
• the greater the difference in temperature, the faster the rate of cooling will be
• if there's a difference in temperature between two places, then energy will flow between them

Kinetic Theory

kinetic theory can explain the three states of matter

solids

• strong forces of attraction hold the particles close together in a fixed, regular arrangement
• the particles don't have much energy so they can only vibrate about their fixed positions
• if you heat the solid eventually the solid will melt and become liquid

liquids

• there are weaker forces of attraction between the particles
• the particles are close together, but can move past each other and form irregular arrangements
• they have more energy than the particles in a solid- they move in random directions at low speeds
• if you heat the liquid, eventually it will boil and become gas

gases

• there are almost no forces of attraction between the particles
• the particles have more energy than those in liquids and solids
• they are free to move and travel in random directions and at high speeds

Conduction

conduction occurs mainly in solids

• in a solid, the particles are held tightly together. So when one particle vibrates, it bumps into other particles nearby and quickly passes the vibrations on
• particles which vibrate faster than others pass on their extra kinetic energy to neighbouring particles.
• these particles then vibrate faster themselves
• this process continues throughout the solid and gradually the extra kinetic energy is spread all the way through the solid
• this causes a rise in temperature at the other side
• conduction of heat is the process where vibrating particles pass on extra kinetic energy to neighbouring particles
• metals conduct heat really well because some of their electrons are free to move inside the metal
• heating makes the electrons move faster and collide with other free electrons, transferring energy
• these then pass on their extra energy to other electrons
• because the electrons move freely, this is a much faster way of transferring energy than slowly passing it between jostling neighbouring atoms
• most non-metals don't have free electrons, so warm up more slowly, making them good for insulating things
• liquids and gases conduct heat more slowly than sloids
• …