Energy Chapter 2 Section 1

2.1 Objective Questions Explain how energy is involved in every change in matter. Explain how the law of conservation of energy applies to changes in matter. How are heat and temperature different? What is the relationship & differences between the Celsius & Kelvin temperature scales?

Review Physical changes – a change of matter from one form to another without a change in chemical properties Chemical changes – change into an entirely new substance with different properties Physical Changes (affect only the physical properties of matter)

Energy & Change All physical & chemical changes involve a change in energy. Energy – capacity to do work Sometimes energy must be supplied for a change in matter to occur. Evaporation – a change from liquid to gas Many changes also require the release of energy. Energy is released when vapor returns to liquid

Practice Break The capacity to do work is ___________. A change in matter from one form to another without a change in chemical properties is a _________ change. A change that occurs when one or more substances change into new substances with different properties is a ________ change.

Practice Break The capacity to do work is energy. A change in matter from one form to another without a change in chemical properties is a physical change. A change that occurs when one or more substances change into new substances with different properties is a chemical change.

Energy & Change Endothermic – process where energy is absorbed Ex. melting ice, liquid to gas Exothermic – process where energy is released Ex. freezing, gas to liquid

Energy & Change Law of the conservation energy energy cannot be created or destroyed During any physical or chemical change the total energy remains constant. The energy changes from one form to another.

Energy & Change System – all of the components that are being studied at a given time Surroundings – everything outside the system Energy is often transferred between a system & its surroundings.

Heat Heat – energy transferred between objects that are different temperatures Energy is always transferred from a warmer object to cooler one.

Heat Temperature – a measure of how hot or cold something is A measure of the average kinetic energy of the particles in an object Kinetic energy – energy due to an objects motion

Practice Break #2 A change in matter in which energy is absorbed is a(n) __________ process. A change in matter in which energy is released is a(n) __________ process. Energy must be added to a solid to melt it. This addition gives the particles ________ energy, allowing them to move out of the crystalline structure. To freeze a substance energy must be __________ from the substance.

Practice Break #2 A change in matter in which energy is absorbed is a(n) endothermic process. A change in matter in which energy is released is a(n) exothermic process. Energy must be added to a solid to melt it. This addition gives the particles kinetic energy, allowing them to move out of the crystalline structure. To freeze a substance energy must be transferred from the substance.

Measuring Temperature Fahrenheit , Celsius, & Kelvin The Fahrenheit scale is not used in chemistry. SI unit for temperature – Kelvin, K The zero point on Celsius scale is the freezing pt. of water The zero point on the Kelvin scale is absolute zero - (minimum average kinetic energy).

Celsius & Kelvin To change from Kelvin to Celsius ˚C = K – 273.15 To change for Celsius to Kelvin K = ˚C + 273.15

Practice Break #3 100˚C = ______ K 293.15 K = ______ ˚C

Practice Break #3 100˚C = 373.15 K 293.15 K = 20˚C 55˚C = 328.15 K

Heat When can heat be transferred and not increase the temperature? When the energy is being used during a physical change.

Heating Curve

Specific Heat The relationship between energy transferred as heat to a substance & the substance’s temperature change. The amount of heat required to raise the temperature of 1g of a substance by 1K or 1˚C. SI units – J/g∙K or J/g∙˚C