Energy and Reactions

matter and energy

matter: anything that has mass and takes up space

energy: ability to do work or cause change

energy is used anytime a change in matter occurs

energyEnergy is the ability or

the potential to make something happen (do work); that is to move or to change a property of matter

many forms mechanical thermal electromagnetic electrical chemical

changes in matter

Energy is used anytime a change in matter occurs

two kinds changes in matterphysical changeschemical changes

physical change

alters form or appearance of material, but does not change material into brand new substance

examples chopping wood bending wire molding clay

chemical change

produces new substances

examples wood burning sour milk

Chemical reactions occur when bonds between the outermost (valence) electrons are formed or broken

Chemical Chemical ReactionsReactions

Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.

Chemical Chemical ReactionsReactions

The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2 CO2, contains the same information as a sentence but has quantitative meaning as well.

Chemical Reaction Chemical Reaction Equations Equations

H2 + Cl2   -->   2 HCl

Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction

Chemical Reaction Chemical Reaction Equations Equations

H2 + Cl2   -->   2 HCl

– Chemical equations show what enters the reaction - reactants (the molecules shown on the left of the arrow) and what comes out of the reaction - products (the molecules shown on the right of the arrow).

Chemical ReactionChemical ReactionEquationsEquations

Chemical Reaction Chemical Reaction Equations Equations

H2 + Cl2   -->   2 HCl

reactants  -->   products

Subscripts vs. Subscripts vs. CoefficientsCoefficients

The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

4 Al + 3 O4 Al + 3 O22 ---> 2 Al ---> 2 Al22OO33

This equation meansThis equation means

4 Al atoms + 3 O4 Al atoms + 3 O22 moleculesmolecules

---produces--->---produces--->

2 molecules of Al2 molecules of Al22OO33

Chemical EquationsChemical Equations

Endergonic & Endergonic & Exergonic reactionsExergonic reactions

EndergonicEnergy IN

Putting together bonds

Exergonic Energy OUT

Breaking bonds apart

Endergonic or Exergonic reactions?

What types of energy?

Endergonic & Exergonic reactions

vs. Endothermic & Exothermic

reactionsTherm – heat Ergon – any type of energy

so Endothermic reaction is a type of endergonic reaction

Endergonic reaction – any type of energy taken inEndothermic reaction – only heat energy taken in

Exergonic reaction – any type of energy given offExothermic reaction – only heat energy given off