Day 1 Please get a computer up and running. Launch molecular workbench Objectives: –Explain the difference between heat and temperature –Explain the three main methods of heat transfer from an atomic perspective

What is thermodynamics? Thermodynamics is the study of the relationship of heat to work and energy. This is typically studied while looking at a particular system. System - A defined portion of the universe to be studied. A system can be anything - piston, test tube, living thing, or a planet. Work - A push or pull which causes movement. Energy – The ability to do work. There are several forms of energy: Kinetic, Potential, Electromagnetic and Mechanical are the most commonly discussed.

Energy Flow Energy moves from one system to another because of differences between systems. If you have two identical systems with equal amounts of energy, there will be no flow of energy. When you have two systems with different amounts of energy the energy will start to flow spontaneously from high to low. Regions of high pressure air forces large numbers of molecules into areas of low pressure.

Energy Flow Areas of high temperature give off energy to areas with lower temperature. The bigger the differences in energy, the faster it will flow from one area to another. The flow of energy that causes a change in an object’s temperature is called heat. This means that if there is no change in temperature, there is no heat.

Heat vs. Temp Heat is the transfer of energy which causes a change in temperature. Temperature is a measure of the kinetic energy of the atoms in a sample. So, heat flow causes a change in the kinetic energy of particles. Heat can transfer in three ways. Two require physical contact between materials with different temperatures, the third does not.

Log into your MW account Complete the online activity: Heat Intro

Day 2 Schedule: –Finish MW activity –Review heat transfer –Introduction to measuring heat transfer Objectives –Explain the three main methods of heat transfer from an atomic perspective –Calculate heat transfer

Heat Transfer

Conduction

Heat flows via collisions between atoms in immediate contact. This causes heat to transfer in a linear fashion, those closest to the heat source heating first and those farther out later. Occurs in solids. Materials that are good at transferring heat this way are considered good conductors of heat. Materials that are not good at transferring heat this way are considered insulators.

Convection

In fluids (liquids, gases and plasmas), since the atoms can flow, they can carry their kinetic energy around with them. Since heating a group of atoms creates more collisions, they are forced farther apart, increasing their volume. This makes them less dense, causing them to float on the more dense, closer packed atoms.

Convection The less dense, higher energy group of atoms will rise, carrying their energy with them. As they bump into other atoms, they will transfer their energy, eventually slowing down and becoming more dense. This causes them to sink back down. This rising and sinking creates a flow of atoms called convection currents.

Convection These currents cause everything from movement of the earth’s tectonic plates to ocean and global air currents.

Radiation

Convection and conduction transfer kinetic energy through direct collisions between matter. Radiation is a transfer of energy without direct contact. Radiation transfers pure energy, a kind of electromagnetic (EM) wave, that does not need anything else to carry it. When the EM wave strikes a surface, atoms absorb the energy and convert it to kinetic energy.

Measuring Heat Transfer To calculate the amount of energy transferred into or out of a system, we use temperature change. Since temperature measures kinetic energy, and heat transfer changes kinetic energy, temperature change is a direct measurement of energy in or energy out. However, we need two more pieces of information to calculate heat transfer.

Measuring Heat Transfer Since each atom needs to absorb energy to gain KE, more atoms require more energy to increase their energy. This means that mass is a key component for calculating energy transfer. More atoms/ mass needs more energy to change the average KE, and vice versa.

Measuring Heat Transfer Some materials change their KE more easily than others. The measure of this ease of change is called an object’s ‘specific heat.’ A lower specific heat means it is easier to change its KE.

Measuring Heat Transfer These three pieces of information- temperature change, specific heat and mass – allow us to determine energy transfer. We use a simple equation to find the heat transfer. Each piece of information is given a variable to make the equation easier to write. q = heat m = mass c = specific heat ΔT = temperature change

Measuring Heat Transfer

A note about units for heat –One of the first units for measuring heat was the calorie. –It was defined as the amount of energy needed to heat one gram of water by one degree Celsius. –A food Calorie is equal to 1000 of these calories, or is a kilocalorie.