THE ABILITY TO CAUSE CHANGE 1

Energy Changes UNIT 3 Energy changes are involved in every chemical reaction—even those that occur in our bodies. While many processes involve the release of energy, others are accompanied by the absorb energy. Sarah Reinertsen is a competitive runner. She relies a great deal on energy produced by the chemical reactions in her cells. Chapter 5: Energy Changes

UNIT 3 Section 5.1 The Nature of Energy and Heat Chapter 5: Energy Changes Burning wood involves changes to the matter that make up the wood. A change in energy content also occurs. Energy is released, mostly as heat and light. Chemical and physical changes in matter involve changes in energy content. These changes in energy involve the release or absorption of energy.

UNIT 3 Section 5.1 Two categories of energy Chapter 5: Energy Changes Kinetic Energy energy of motion anything moving has kinetic energy Potential Energy stored energy due to the condition or position of the object SI unit of energy is the joule, J (1 kJ = 1000 J) 1 calorie = 4.18 Joules 1 kcal = 1000 cal

Definitions for units Calorie – measure of how much energy is required to heat one gram of water 1 ̊C. Joule – another unit of measurement for energy SI – international standard for measurement using the metic system.

Heating Curves The temperature of most pure substances is constant during a phase change.

Cooling Curves The temperature of most pure substances is constant during a phase change.

Chemical Reaction (change) when new substances are produced. Bonds ARE broken.

Chemical Energy energy stored in the bonds of molecules. Fuel Molecule that stores chemical energy in its bonds.

Conservation of EnergyEnergy cannot be created or destroyed…only changed from one form to another. The total energy of an isolated system remains constant (isolated systems have no external forces and no mass changes) 13

14 ENERGY BEFORE = ENERGY AFTER Energy can be changed from one form to another, but it does not disappear.

Practice calculations 3.78 calories = ? Joules (1 calorie = 4.18 J)

Practice Calculation 9,427 J = ? Kcal 1 kcal = 1000 cal 1 cal = 4.18 J

Practice Calculation 10.4 Kj = ? K cal1 cal = 4.18 J 1 kcal = 1000 cal 1 kj = 1000 J

Practice Calculation 3.21 x 10⁻⁵ kcal = ? Kj1 cal = 4.18 j 1 kcal = 1000 cal 1 kj = 1000 J