Chemistry Physical, Chemical, and Nuclear Changes (continued)

Transcription

1 Chemistry 1010 Physical, Chemical, and Nuclear Changes (continued)

2 Review What type of change is occurring in the following situations? whittling a stick of wood physical change carbon-14 in a wooden artifact decaying to nitrogen-14 nuclear reaction burning wood in a campfire chemical reaction

3 What kind of change is taking place in each of the following equations? What does each represent? C 3 H C H 2 chemical reaction propane burning 238 U 234 Th + 4 He nuclear reaction uranium decaying in uranium marbles C 9 H 8 (l) C 9 H 8 (g) physical change cinnamaldehyde evaporating

4 Types of Physical and Nuclear Reactions There are two main types of physical changes that are commonly described by an equation in chemistry. What are they? 1) changes of state H 2 (s) H 2 (l) 2) dissolving C 11 H H 2 C 11 H 22 11(aq)

5 There are three common types of nuclear reactions. Where do each of these occur? 1) fusion atoms are joined together to make larger ones in stars in particle accelerators 2) fission large, unstable atoms are split apart in nuclear weapons in nuclear power plants

6 3) radioactive decay a small piece of the nucleus of an atom is ejected naturally occurring radioisotopes inside nuclear reactors nuclear waste Label the following reactions as fusion, fission, or radioactive decay. 236 U 90 Sr Xe + 3 n o fission 255 Fm 251 Cf + 4 He 209 Bi + 64 Ni 273 Rg radioactive decay fusion

7 Clues that a chemical reaction is happening How can you recognize a chemical reaction if you have an equation? C 3 H C H 2 new compounds are formed chemical bonds are broken and formed If you don't know what the equation is, how can you tell? look for clues that new compounds are formed, or that chemical bonds are being broken and formed

8 What kind of clues? Clue #1 new compound forming that is a gas antacid tablet + stomach acid What gas is being formed? gas formed CaC HCl CaCl 2 + H 2 + C 2(g) antacid stomach acid gas Can you think of anything else that bubbles?

9 Clue #2 new compound forming that is a solid solution 1 + solution 2 What new compound is being formed? precipitate forms NaCl (aq) + AgN 3(aq) NaN 3(aq) + AgCl (s) table salt in water silver nitrate in water sodium nitrate in water silver chloride precipitate Can you think of anything else that forms a solid?

10 Clue #3 new compound formed that is a different color solution 3 + solution 4 What is the yellow solid? bright yellow solid KI + Pb(N 3 ) 2 KN 3 + PbI 2 potassium iodide lead nitrate potassium nitrate lead iodide yellow solid Can you think of anything else that changes color?

11 Clue #4 heat or light is released strong acid + strong base + heat What reaction is happening? HCl + NaH NaCl + H 2 + heat strong acid strong base Can you think of anything else that releases light or heat?

12 Now that you know the clues, you are ready to make some educated guesses about everyday processes. Which are chemical reactions, and which are not, and why? Rolls brown in the oven. A red shirt fades in the sun. Detergent washes grease off of pans. Copper roof tiles turn greenish over time. Cement dries and hardens. Silver candlesticks tarnish. Silver polish removes the tarnish. chemical color change chemical color change physical grease dissolves chemical heat released chemical color change chemical color change physical dissolving ne drop of food coloring turns the whole bowl of frosting red. physical mixing An acidic cleaner removes hard water deposits. Food is digested. chemical color change chemical gas is released

13 Bleach removes a grass stain. Hydrogen peroxide bubbles when poured on a cut. A microwave heats a hot dog. Candle wax melts. A candle burns wax. Meat turns brown when you cook it. Plants make sugar and oxygen from carbon dioxide and water. Hot hands get warm when bent. ld wine turns into vinegar. chemical color change physical change of state chemical heat released chemical color change chemical heat released chemical new smell Paint remover loosens paint so it can be removed. chemical gas is released physical (unless it turns black) chemical new compounds physical paint dissolves

14 Balancing chemical reactions When we write a chemical reaction, it is important to know how many units of each compound are needed. hydrogen burning What are the reactants and products? hydrogen + oxygen water What are the formulas for these molecules? H H 2 What's wrong with this? + Where did the other oxygen go?

15 How do we fix it? + use two hydrogen molecules and make two water molecules What does the new equation look like? 2 H H 2 Why can't we just alter the formula? H 2 + H 2 NPE! oxygen doesn't exist that way

16 In order to make sure that the equation works, make sure there are the same number of atoms of each element at the beginning and at the end of the reaction. reactants products original equation: H H 2 H H :( + new equation: 2 H H :) +

17 Let's try another example. antacid + stomach acid CaC HCl CaCl 2 + H 2 + C 2 reactants Ca C H Cl X X products Ca C H Cl

18 Try another: propane burning reactants products C 3 H C 2 + H 2 C 3 H C 2 + H 2 C 3 H C 2 + H C H C H X X X X X C 3 H C H

19 ne more: iron rusting reactants products Fe Fe 4 Fe Fe