1. Chapter 5.1
Chemical Reactions

2. Chemical reactions change substances
When sugar, water, and yeast are mixed with flour to make bread dough, a chemical reaction takes place
Yeast acts on sugar to form carbon dioxide and lactic acid
Different from sugar
Sugar is sweet, lactic acid is sour
Chemical reactions occur when substances undergoe chemical changes to form new substances (pg 148)

3. Chemical reactions change substances
Production of gas and change of color are signs of chemical reactions
In bread, the carbon dioxide gas produces expands the dough
As the dough bakes, old bonds break and new bonds form
Reactions involving starch and protein make food turn brown when heated (pg149)

4. Chemical reactions change substances
Chemical reactions rearrange atoms
When gasoline is burned, lots of chemical reactions occur
Isooctane, C8H18, and oxygen, O2, are the reactants
They react and form two products, carbon dioxide, CO2, and water, H2O
The products and reactants contain the same types of atoms: carbon, hydrogen, and oxygen
Atoms are rearranged as bonds are broken and formed
Mass is conserved (pg 149)

5. Energy and Reactions Energy must be added to break bonds
In each isooctane molecule, the bonds to carbon are covalent
A double covalent bond holds the two oxygen atoms together
For the atoms in isooctane and oxygen to react, all of these bonds have to be broken
This takes energy (pg149)

6. Energy and Reactions Forming bonds releases energy
Once energy is added to start the isooctane-oxygen reaction, new bonds form to make the products
When new bonds form, energy is released
When gasoline burns, energy in the form of heat and light is released (pg 150)

7. Energy and Reactions Energy is conserved in chemical reactions
The energy released during the reaction is stored in the reactants
Stored energy is called chemical energy
Total energy before the reaction is equal to the total energy of the products (pg 151)

8. Energy and Reactions Reactions that release energy are exothermic
The isooctane-oxygen reaction releases more energy than is absorbed to break the bonds in the reaction
This is an exothermic reaction
Temperature of surroundings rises because energy is released (pg 151)

9. Energy and Reactions Reactions that absorb energy are endothermic
If hydrated barium hydroxide and ammonium nitrate are combined, the reaction between them absorbs so much energy from the surroundings that the water vapor in the air will condense and freeze to the surface of the flask
Endothermic reaction (pg 151)

10. Energy and Reactions
Some endothermic reactions cannot get enough energy from the surroundings, so energy must be added to get the reaction started
Photosynthesis is an endothermic reaction
Plants use light energy convert carbon dioxide and water to glucose and oxygen (pg 152)