Chemical Reactions Chapter 13

Homework Assignment Chap 13 Review Questions (p 290): 1 – 23 Multiple Choice Questions:

3 ways of representing the reaction of H 2 with O 2 to form H 2 O Chemical reaction - process in which one or more substances is changed into one or more new substances. reactantsproducts Chemical equation - uses chemical symbols to show what happens during a chemical reaction

How to “Read” Chemical Equations 2 H 2 (g) + O 2 (g) 2 H 2 O (l)

How to “Read” Chemical Equations 2 molecules H molecule O 2 makes 2 molecules H 2 O 2 moles H mole O 2 makes 2 moles H 2 O IS NOT 2 grams H gram O 2 makes 2 g H 2 O 2 H 2 (g) + O 2 (g) 2 H 2 O (l)

Chemical reactions only involve the rearrangement Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions. Chemical equations must be balanced! Chemical equations must be balanced!

Balancing Chemical Equations Methane reacts with oxygen to form carbon dioxide and water Change the numbers in front of the formulas (coefficients) to make the number of atoms of each element the same on both sides of the equation. Do not change the subscripts. 2H 2 O NOT H4O2H4O2 CH 4 (g) + O 2 (g) → CO 2 (g) + H 2 O (l) CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (l)

Fe (s) + O 2 (g) → Fe 2 O 3 (s) 4Fe (s) + 3O 2 (g) → 2Fe 2 O 3 (s) Examples of balancing equations H 2 (g) + N 2 (g) → NH 3 (g) 3H 2 (g) + N 2 (g) → 2NH 3 (g)

Acids Have a sour taste. Vinegar owes its taste to acetic acid. Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gas. Cause color changes in plant dyes. Cause color changes in plant dyes. 2HCl (aq) + Mg (s) MgCl 2 (aq) + H 2 (g) 2HCl (aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O (l) Aqueous acid solutions (aq) conduct electricity. Aqueous acid solutions (aq) conduct electricity.

Have a bitter taste. Have a bitter taste. Feel slippery. Many soaps contain bases. Feel slippery. Many soaps contain bases. Bases Cause color changes in plant dyes. Cause color changes in plant dyes. Aqueous base solutions (aq) conduct electricity. Aqueous base solutions (aq) conduct electricity. ammonia hydroxide ion

(“milk of magnesia”)

acid - a hydrogen ion donor base - a hydrogen ion acceptor acidbase A hydrogen ion, H +, is the same as a proton!

Hydronium ion, hydrated proton, H 3 O + Electron-rich region Electron-poor region Figure 13.3 H H H O

acid base acid - a hydrogen ion donor base - a hydrogen ion acceptor acid base

Neutralization Reaction acid + base salt + water HCl (aq) + NaOH (aq) NaCl (aq) + H 2 OSalts HCl (aq) + KOH (aq) KCl (aq) + H 2 O