Energy and Chemical Change Chapter 16 Energy and Chemical Change

Energy Energy is the ability to do work or produce heat. Can you name some examples of energy that you observe in your everyday life? Heat is a form of energy that flows from a warmer to a cooler object. James Prescott Joule was the first person to make the connection between work and heat which ultimately lead to the Law of Conservation of Energy. Using a simple machine, Joule was able to calculate the amount of heat produced by mechanical energy. The amount of heat required for work done is called the Joule (J). It takes 4.184 joules to move one kilogram of mass a distance of one meter in 1 second.

Types of Energy There are 2 different forms of energy : Kinetic and Potential Potential is due to the composition or position of an object. Kinetic is energy of motion

Kinetic and Potential Energy on a Molecular Level The potential energy is locked in the bonds that hold atoms together in compounds The kinetic energy occurs when the chemical bonds separate Bond Energy (hehehehehe)

Chemical Potential Energy The amount of energy stored in a substance. The atoms and type of bond present in the compound determine the chemical potential energy. In octane C8H18, the energy is related to the strength found between the carbon and hydrogen bonds. When the fuel is burned in an engine, the stored energy is converted to work in moving the pistons which ultimately moves the wheels and propels the car forward. Diesel fuel (C12H23) has more Chemical Potential Energy than octane, and as a result, can achieve the same gas mileage as small economy octane powered cars.

Law of Conservation of Energy The Law of Conservation of Energy states that the energy in the universe is constant. As energy changes from one form to another, there is no net gain or loss of energy. This explains why perpetual motion machines are a myth. As machines are set in motion, there is a heat loss due to friction and heat between mechanical parts and eventually the machine will come to a stop once its energy has been converted into other forms. A car engine only converts about 37% of the energy in gasoline to mechanical energy to turn the wheels. The other 63% goes to energy in gasoline lost as heat. All the metal to metal contact in an internal combustion engine causes friction.

Measuring Heat Because energy and heat go hand in hand, the flow of energy and the resulting change in temperature is measured in the metric system with joules. Also, a method of measuring heat and energy that is commonly used is the calorie- the amount of heat needed to raise the temperature of one gram of pure water one degree centigrade. Another area the term calorie is used is with food. It takes 1000 calories to equal one food Calorie. All of these terms are related and to satisfactorily complete this chapter, you will need the following equivalents memorized: 1000 calories = 1 Calorie = 1 kilocalorie 4.184 joules = 1 calorie 1000 joules = 1 kilojoule

Heat Problems Practice I Convert 10 calories to joules 2. Convert 10 joules to calories 3. Convert 3000 joules to kilojoules 4. Convert 3000 calories to kilocalories

Heat Problems Practice I 5. Convert 3000 calories to Calories 6. Convert 3000 calories to kilojoules 7. Convert 3000 joules to kilocalories 8. Convert 3000 joules to Calories

Heat Problems Practice I 9. Convert 10 kilojoules to kilocalories 10. Convert 10 Calories to kilojoules 11. Convert 3000 calories/minute to joules/hour 12. Convert 10 kilojoules/minute to kilocalories/hour