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

energy Energy 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 matter physical changes chemical 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 Reactions

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

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 + O 2  CO 2, contains the same information as a sentence but has quantitative meaning as well.

Chemical Reaction Equations H 2 + Cl 2 --> 2 HCl Symbols represent elements, formulas describe compounds, chemical equations describe a chemical reaction

Chemical Reaction Equations H 2 + Cl 2 --> 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 Reaction Equations

H 2 + Cl 2 --> 2 HCl reactants --> products

Subscripts vs. Coefficients 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 O 2 ---> 2 Al 2 O 3 This equation means 4 Al atoms + 3 O 2 molecules ---produces---> ---produces---> 2 molecules of Al 2 O 3 2 molecules of Al 2 O 3 Chemical Equations

Endergonic & Exergonic reactions Endergonic Energy IN Putting together bonds Exergonic Energy OUT Breaking bonds apart

Endergonic or Exergonic reactions? What types of energy?

Endergonic & Exergonic reactions vs. Endothermic & Exothermic reactions Therm – heat Ergon – any type of energy so Endothermic reaction is a type of endergonic reaction

Endergonic reaction – any type of energy taken in Endothermic reaction – only heat energy taken in Exergonic reaction – any type of energy given off Exothermic reaction – only heat energy given off