Chemical ChangeChapter 3

Section 3.1

Identify important reactions in society Recognize and identify evidence for

chemical changes Differentiate between endothermic and

exothermic reactions Describe the Law of Conservation of Mass

Objectives

What is the difference between a chemical and physical change?

◦ Chemical change- something new is created with its own unique properties

◦ Physical change- nothing new is created (just changing states) What are the three states?

To Start

Which of the following are chemical changes? Physical changes?

Chemical or Physical?

Reactant + reactant product(s) Products have different properties than

reactants◦ Properties include: state at RT, temperature,

melting point, color and density Includes a flow of energy

◦ IMPORTANT: drives chemical reactions Can be fast or slow

Chemical Change

Batteries Combustion Engine Wine production Baking bread Photosynthesis Cellular respiration (making energy in our

bodies)

Examples of Chemical Reactions

What are ways that we know a chemical change has occurred?◦ Formation of a gas (bubbles)

Air bag inflation in a car◦ Color change

Sugar and sulfuric acid◦ Formation of a precipitate (change in state)

Mixing silver nitrate with sodium chloride◦ Flow of energy (usually detected as a change in

temperature) Combustion (lighting a match)

Evidence of a Chemical Change

What will happen when I add baking soda to vinegar in this beaker?

What will happen to the balloon placed over the top?

What gas is produced?

What other examples do we have of a formation of a gas?

Formation of a Gas: Demo

Two types of energy changes:

◦ Exothermic- release of energy (*exit)◦ Endothermic- absorption of energy (*enter)

What change of temperature would you feel with each of these processes?

Can physical changes be exothermic and endothermic? Why or why not?

Energy Changes

Release energy, usually as:◦ heat (flame)◦ light (bioluminescence) ◦ Electricity (battery)

Important ex.: Combustion◦ What is combustion?

Combustion- oxygen reacts rapidly with another substance, releasing energy (burning)◦ 2C6H14(l) + O2(g) 12CO2(g) + 14H2O(g) + energy◦ (Combustion of hexane)

Exothermic Reactions

Absorb energy Ex. Cold packs- squeeze package, breaks

pack inside which keeps chemicals separate; absorb energy and whole mixture cools down

Ex. Photosynthesis◦ Energy + 6CO2(g) + 6H2O(l) C6H12O6(aq) + 6O2(g)

Endothermic Reactions

They may be endothermic or exothermic They are almost always helped by enzymes

(biological catalysts) Catalysts are chemicals that speed up a

reaction but are not used up by it. Photosynthesis and Cellular Respiration

Biochemical Reactions

Developed by Antoine Lavoisier Total mass of the reactants equals the

total mass of the products Using this, we can deduce that:

◦ ** total # of atoms present before a reaction equals the total # of atoms after a reaction

Law of Conservation of Mass

If I get 13 g of H2O and 15 g of NaCl from the reaction of HCl and NaOH, how much NaOH did I use, if I used 10 g of HCl?

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

10g ? 13g 15g

Answer: 18 g

Example