Energy and the Transfer of Heat Photo by ScheiderMac Energy and the Transfer of Heat Photo by Dinshaw Dadachanji

Kinetic Energy Potential Energy There are two basic categories of energy Kinetic Energy Potential Energy & What kind of energy is kinetic energy? Kinetic energy is the energy of motion. What kind of energy is potential energy? Potential energy is stored energy.

Gravitational Potential Energy You have learned about kinetic and potential energy before, but it was in a different context than we will discuss in chemistry. Kinetic Energy Gravitational Potential Energy In this example, the ball has potential energy as it rests on the edge of the ramp. This is converted to kinetic energy as it rolls down the ramp.

But what is this ball made out of? In this context, the system we are studying is the entire ball: the kinetic and potential energies of the ball as a whole. But what is this ball made out of? Individual atoms, ions and molecules. Every particle in the ball is moving, and there is energy stored in the chemical bonds between these particles. This is called its internal energy, and it is was we will be focusing on in chemistry.

So how do we solve this problem? As you have already learned, atoms and molecules are in constant motion. This energy of motion is still referred to as kinetic energy. Now we are worried about the movement of each molecule internally, not the entire object. We cannot measure the motion of particles the same way we would with a large ball. So how do we solve this problem?

You take the temperature! Temperature measures the average kinetic energy of the particles in a system. The higher the temperature, the faster the particles are moving.

While there are 3 major temperature scales, only 2 of these are commonly used by scientists: Celsius and Kelvin are the temperature scales used by most scientists. While you are familiar with Fahrenheit, it is not a widely used scale for science. 7

Converting between Kelvin and Celsius is very simple. 0oC = 273 K Kelvin = oC + 273 The temperature in Kelvin is always 273 degrees higher than the same temperature measured in Celsius.

Convert the temperatures on your notes between Celsius and Kelvin. 373 127 293 77 258

Chemical bonds hold atoms Photo by Peter Murray-Rust It requires energy to form a chemical bond, and this energy is stored in the chemical bonds of compounds and can be released when it is broken. Chemical bonds hold atoms together in molecules The energy stored in the bonds between atoms and ions is known as chemical energy. Because chemical energy is stored energy, it is simply a specific form of potential energy.

Kinetic Energy + Potential Energy = Thermal Energy The kinetic energy and potential energies within an object can be added together to find the total internal energy. The sum of the internal kinetic and potential energies of a system is known as the thermal energy of the system. Kinetic Energy + Potential Energy = Thermal Energy

Heat = (mass)(specific heat)(change in temperature) The thermal energy that is transferred from one object to another is called HEAT! q In chemistry, heat is represented by the letter ____, and the amount of heat transferred between objects is calculated by the formula below: Heat = (mass)(specific heat)(change in temperature) Q = (m)(Cp)(ΔT) Important Fact: All kinds of energy, including heat, are recorded in units of _______. Joules

This will affect whether your final answer is In equations, Δ = (Final) – (Initial) ΔT = (Final Temperature) – (Initial Temperature) This will affect whether your final answer is positive or negative. If your answer is positive, the temperature increased and heat was gained. If your answer is negative, the temperature decreased and heat was lost.

+Q means heat was gained The piece of iron shown below underwent the temperature change to the right. The specific heat of iron is 0.450 J/g●oC. Calculate the change in thermal energy, and decide if heat was gained or lost. Q = (121 g)(20.oC)(0.450 J/g●oC ) Q = 1089 J = 1100 J (sig figs) +Q means heat was gained Initial temperature Final temperature

Transmitting Heat THROUGH Objects Heat passes through solids by the process of ___________. This happens when the particles in the solid bump into each other and pass the energy. conduction

Transmitting Heat THROUGH Objects Fluids, which are _______ and ______ , are able to pass with through the process of __________ because they can _____. liquids gases convection flow

As the temperature of matter increases, Remember: As the temperature increases, the particles move faster. They travel farther and run into each other more often. For these reasons, they spread out or _______. expand As the temperature of matter increases, its particles expand! This makes the matter LESS dense!

You need to understand that as the temperature decreases, the particles move slower. This causes the particles to draw closer together or ________. contract Cooling matter makes it MORE dense!

When things are heated, they expand When things are heated, they expand. This makes them less dense so they rise/float. When they cool, they condense. This makes them more dense so they sink. This pattern will continue in a fluid that has a constant heat source, and it is known as a __________________. convection current

Transferring Heat BETWEEN Objects Whenever heat is passed between two objects that are in direct contact, the heat is primarily transferred through the process of ____________. conduction It does NOT matter what state of matter the two objects are in. When they bump into each other, they pass heat through the process of conduction. Heat travels from the glass container to the water through the process of conduction. Photo by Markus Schweiss

Transferring Heat BETWEEN Objects Whenever heat is passed between two objects that are NOT touching, the heat is transferred through the process of _________. radiation

Radiation is the transfer of heat through electromagnetic waves Radiation is the transfer of heat through electromagnetic waves. Every object emits radiation. The hotter the object, the more radiation it emits. Electromagnetic waves can pass through a vacuum. Because of this, all of the energy we receive from the sun is in the form of radiation.

Important Fact Colors that are ________ absorb more radiation than brighter colors. _______ absorbs the most radiation. This is why you get hotter in the summer when you wear a black t-shirt instead of a white one. darker Black

Important Vocabulary __________ slow down the flow heat. They do NOT stop heat flow, they just slow it down. They keep hot things _____ and cold things ______. Insulators hot cold