# Law of Conservation of Energy

## Presentation on theme: "Law of Conservation of Energy"— Presentation transcript:

Law of Conservation of Energy
States that energy can neither be created or destroyed or that the total amount of energy in a system remains constant. We can measure the energy in terms of calories.

Calories One calorie is defined as the amount of energy needed to raise the temperature of 1 gram of water 1oC Abbreviated as (cal) Dietary calories (C) = 1000cal or 1kcal = amount of energy released from foods

Heat Energy Heat - a flow of energy from a hot object (higher energy) to a cold object (lower energy).  The most familiar form of energy All matter contains some heat energy. The net energy transferred from or to an object as a result of a temperature difference which results in a change in internal energy

Review Heat Energy The heat energy of a substance is determined by how active its particles (atoms and molecules) are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object's molecules and atoms will be less excited and show less movement.

What is Heat Energy? As heat is added to an object the temp. increases
The added heat becomes part of the object’s internal energy

Heat travels from a hot object (higher energy) to a cold object (lower energy).
So how does heat travel from one object to another? By Convection, Conduction and Radiation.

Heat Transfer by Convection
Convection occurs only in liquids and gases.  We call liquids and gases fluids.  It cannot happen in solids.  It needs particles to be free to move about. A radiator in a room heats up the room by convection (NOT radiation).

Heat Transfer by Convection
Look at the engine at the left. Water carries heat from a hot engine through a pump and delivers it to a radiator, whose duty is to give up heat to the air.

Heat Transfer by Conduction
The process in which heat passes through a solid substance is called conduction.  Metals are good conductors of heat.  Non-metals are generally bad conductors of heat.  Liquids and gases are bad conductors of heat as well.  A bad conductor of heat is called an insulator.

Ability of a metal to conduct heat?
What is an element of metal made of? Atoms that vibrate Free electrons that move around They are constantly vibrating or oscillating against each other. Through these collisions, the heat energy is conducted

Heat Transfer by Conduction
The flow of heat from a hot part of a body to a cooler part, without transfer of matter. Can also take place from one body to another, provided the two bodies are in contact, and a temperature difference exists between them. A pot on a hot plate is heated by conduction from the stove surface, via the underside of the pot.

The easiest way to explain heat transfer by RADIATION is by the heat we feel from the sun or a light bulb. RADIATION of heat is the transfer of heat energy through matter or space as electromagnetic waves. Examples : Electromagnetic waves called infra-red radiation that is emitted from earth. Ultraviolet radiation that is emitted from the sun and causes sunburns Microwaves that cook food

Review Heat flows from hot objects to cold objects.
Heat flow depends on the temperature difference. Heat is not temperature. Heat passes by conduction, convection, or radiation. Radiation is caused by infra-red radiation

Determining the amount of heat gained or lost by a substance
Step 1 You will need the following formulas for your calculations: where T refers to the change in temperature Tf refers to the final temperature and Ti refers to the initial temperature

Determining the amount of energy lost or gained
Step 2 where Qcal refers to the heat gained (or lost) expressed in calories mass of water is expressed in grams (1 mL water = 1 gram) T refers to the change in temperature Answers are expressed in calories or cal

45 gm sample of water is heated from 24.0ºC to 82.0 ºC
How much heat was gained by the cold water? ∆T = 82.0 – 24.0 = 58.0 ºC Qcal = 45 g x 58.0 ºC = 2610 = 2600cal

If a sample of hot water and cold water are mixed together…
Based on the Law of Conservation of Energy what would you expect?

110. 5 gm sample of hot water has an initial temp of 61. 8ºC. 250
110.5 gm sample of hot water has an initial temp of 61.8ºC gm of 1.8ºC water is added to it and the final temperature is 6.8ºC 1 - How much heat was gained or lost by the by the cold water? 2 - How much heat was gained or lost by the warm water?

How Do We Measure the Changes in Heat Energy?
Temperature

What is Temperature? The measure of the average kinetic energy of the particles (atoms and molecules) of a substance Kinetic energy is the energy an object posses because of it’s motion

How do we measure temperature?
With a thermometer. 1. A thermometer is an instrument that utilizes the physical property of thermal expansion for the purpose of accurately determining temperature

What is thermal expansion?
The property of a substance to expand with an increasing temperature and contract with a decreasing temperature The expansion and contracting allows for the quantitative measure of temperature by using a thermometer.

Thermometer Most common is the bulb type
As the substance gets hotter, the particles in the liquid mover faster and spread out This causes the red liquid to move up. Gives us a quantitative reading.

3 Different Temperature Scales