ENERGY INTRODUCTION

F. Energy is always involved in physical and chemical change

Energy definition: ability to transfer heat or do work Examples of energy sources

1. Chemical2. Nuclear 3. Kinetic4. Electrical5. Gravity (or

positional)

Heat and temperature are different• Key concept in chemistry

• Heat is a form of energy (measured in joules)

• Temperature is a measure of hotness or coldness (measured in ºC or K)• Actually the average kinetic energy of the atoms

When a scientist heats a substance, she is adding ___________.This results in the atoms in the substance moving ___________ and so the temperature increases.

Comparing °C and K

What about Temperature? We all know that some things feel hot, and others cold, but is there more to temperature than that?

When an object feels hot, the atoms inside it are moving fast in random directions, and when it feels cold, they are moving slowly. Our body interprets that random atomic motion into what we feel as hot and cold, and a thermometer interprets that atomic motion as a certain number of degrees.

So when I'm heating something, I'm just making its atoms move faster?

Exactly. If the object is a solid the atoms are vibrating back and forth, and if it is a gas like the air, the atoms are flying around much like little balls.

Energy, usually in the form of heat, is involved in changes of state (phase changes.)

Heat is __________________. Therefore, it is a _______________ change.

Heat is __________________. Therefore, it is a _______________ change.

Phase change Phase change

Solid

Endothermic – energy absorbed

Exothermic – energy released

Change of State (phase changes)Phase change The change is

called:Is it exothermic or endothermic?

Everyday example

Solid to liquid

Liquid to gas

Solid to gas

Gas to liquid

Liquid to solid

Gas to solid

Changes in StateDo you answers agree with this table?

F. Energy is always involved in physical and chemical change1. Exothermic: We use the words: 2. Endothermic

We use the words:

The Law of Conservation of Energy• Energy is neither _______________ nor ______________ in a chemical reaction.

Formative Assessment• I use the results to help plan lessons for this class

• Do you best

• Full credit for trying

Graphing a heating curve • Graphs in chemistry & science 1. Title2. Label each axis

1. X axis = independent variable (scientist controls) 2. Y axis = dependent variable (resulting values due to the changes

in the independent variable)

3. Units must always be given 4. Line graphs are the most common for experimental data

Heating curve worksheet: X axis = Time Y axis = Temperature

Heating curve - states of matter & phase changes

Animation – heating curve• http://

www.dlt.ncssm.edu/tiger/Flash/phase/HeatingCurve.html

• http://www.chm.davidson.edu/vce/phasechanges/HeatingCurve.html

• http://www.kentchemistry.com/links/Matter/HeatingCurve.htm• Tutorial

Using reference tables in chemistry

• Scientists must be able to interpret and use reference tables.

• This provides information about a substance without the scientist having to make the measurements.

Physical Properties of Matter

• Melting Points• Boiling Points• Density • Solubility

Melting and Boiling Points

• Use the Reference Tables to determine the following:– Rank the following substances from

smallest melting point to largest melting point:

H2O, N2, iron, lead, O2, C12H22O11

Reference Tables con’t• What is the state of matter (solid,

liquid, or gas) will each of the following substances at the given temperature?a. chlorine at -25 oCb. ethanol at 0 oCc. sodium chloride at 1500 oCd. methanol at -100 oCe. sulfur dioxide at 10 oC

Density• Using the reference tables,

determine the following:– Rank the following substances from

greatest density to smallest density:H2O, Mg, C6H14, Pb, methanol, NaCl

Reference Tables con’t• What is the mass of 36.5 mL of

ethanol? • What is the volume of 50.0 g of

molten lead? • You have 100.0 cm3 of glucose and

sucrose. Which sample has the greatest mass? Support answer with calculations.

TEMPERATURE

I

II

III

IV

V

TIME

Heating Curve