Energy Transfer

What’s the difference between temperature & heat?? Temperature is the measure of the average kinetic energy of the particles in a substance.

Temperature unit of measurement is the Kelvin (but you will see Celsius used) a. K = C + 273 (10C = 283K) b. C = K – 273 (10K = -263C) Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

Heat It is measured in joules Common usage is a heat unit called the calorie (the energy needed to raise the temperature of 1 gram of water by 1o C) Chemists use the kilocalorie (1000 calories=4200 Joules) Nutritionists call it a food Calorie

Thermal energy relationships As temperature increases, so does thermal energy (because the kinetic energy of the particles increased). Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

The flow of thermal energy from one object to another. Cup gets cooler while hand gets warmer Heat The flow of thermal energy from one object to another. Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler

Heat Transfer Heat flows from hot to cold. If you hold something cold, heat flows from hand to object. If you hold something hot, heat flows from object to hand Conduction- transfer of thermal energy through matter by the direct contact of particles Occurs because particles are in constant motion

Conduction Heating of metal pan- Particles in handle of pan move slowly Fast moving particles from the bottom bump into slower particles and speed them up Occurs until all particles move the same speed Conduction works best in solids- especially metals- because particles are close together

Conduction and Convection Metals- good conductors-because electrons move easily Fluid- any materials that flows Convection- transfer of energy in a fluid by the movement of heated particles Convection currents transfer heat from warmer to cooler parts of a fluid. Convection vs. Conduction- Conduction involves collisions and transfers of energy. Convection involves movement of the energetic particles from one location to another

Convection Convection- results in changes in density Lava Lamp- As particles move faster, they get farther apart Fluid expands as temperature increases Larger volume = smaller density Decreasing density results in the rise of the warmer fluid Lava Lamp- Cool oil = dense = sits on the bottom Warmer oil = less dense than alcohol & rises As it rises, it loses energy through conduction Causes decrease in density = sinking

lava lamps!

Oil starts to lose heat by conduction and falls Oil is warm, so it rises When oil is cool

Convection Currents Currents in which warm portions of the fluid move through the substance- convection The warm portions transfer energy to the cool section through conduction

Heat Transfer on Earth At equator- earth experiences the most heat from the sun. Result: evaporation of water and large accumulations of clouds. As the water vapor rises, it cools and condenses, forming rain After the rain = dry air Dry air causes moisture to evaporate, drying out the ground – causes desert Convection currents create deserts and rain forests over different regions of Earth

Radiation Transfer of heat to the earth – occurs through radiation Radiation- the transfer of energy by electromagnetic waves. The waves travel through space even without matter

Land heats up and cools down faster than water Specific Heat Some things heat up or cool down faster than others. Land heats up and cools down faster than water

Specific heat is the amount of thermal energy required to raise the temperature of 1 kg of a substance one degree (C or K). This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

Specific Heat The higher the specific heat, the more energy is required to cause a change in temperature. Water is slower to heat but is also slower to lose heat

Why does water have such a high specific heat? water metal Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds and do not need as much energy to break them.

Expansion of Water Remarkably interesting case

Expansion of Water This is why lakes and ponds and rivers freeze with the ice on top If they didn’t, no aquatic life would be possible