Thermodynamics (Ch. 15): Temperature, Heat and Expansion Essential Question: How does heat flow between two objects?

Temperature Temperature is a measure of the average kinetic energy of the particles in a substance. Remember, kinetic energy is the energy an object has due to its motion. The higher the average kinetic energy, the faster the particles move Temperature and Heat are NOT the same thing

Temperature Scales There are 3 types of temperature scales: Fahrenheit (◦F) Celsius (◦C) Kelvin (K)(SI unit)

Heat Heat is energy in transit; thermal energy that flows from something at a higher temperature to something at a lower temperature Heat always transfers from hot to cold the unit for heat is the calorie (C)

Internal Energy Internal (thermal) Energy is the grand total of all energies (kinetic and potential) inside a substance; thermal energy increases as temperature increases (why?)

Specific Heat Specific Heat is the amount of heat needed to raise the temperature of 1kg of a substance by 1°C water has a much higher capacity for storing heat than all but a few uncommon materials Heat is energy. Heat 'passes' due to molecular collisions. Temperature is the measure of molecular kinetic energy, not heat. So, if more heat is needed to raise the temperature of a mole of liquid water one degree than a mole of steam one degree, this means that some of that heat energy is not going into kinetic energy of the liquid water molecules. So what is it going into? It must be going into breaking the hydrogen bonds that water molecules form with each other. This does not happen in ice or steam, since those bonds are not being broken or are already broken. The warmer the water, the more vapour molecules there are breaking those hydrogen bonds (and escaping from the surface). This is why water vapour pressure increases with temperature. 

Thermal Expansion Almost all substances expand when they are heated and contract when they are cooled – exception: water between 0°C and 4°C This is why bridges are built with short segments with small breaks to allow for expansion Joints such as this one are used in bridges to accommodate thermal expansion. Heat is energy. Heat 'passes' due to molecular collisions. Temperature is the measure of molecular kinetic energy, not heat. So, if more heat is needed to raise the temperature of a mole of liquid water one degree than a mole of steam one degree, this means that some of that heat energy is not going into kinetic energy of the liquid water molecules. So what is it going into? It must be going into breaking the hydrogen bonds that water molecules form with each other. This does not happen in ice or steam, since those bonds are not being broken or are already broken. The warmer the water, the more vapour molecules there are breaking those hydrogen bonds (and escaping from the surface). This is why water vapour pressure increases with temperature.