Chemical Reactions Slide 2 Chemical Reactions Change Substances
Chemical Reactions
Slide # 2 Chemical Reactions Change Substances 1. 2. Chemical reactions occur when substances undergo chemical changes to form new substances. Common, every day chemical reactions include: growing, ripening, decomposing, & burning (combustion) Growing Decomposing Ripening Burning
Slide # 3 Signs of Chemical Reactions 1. Bubbles appear. 2. A precipitate (solid) forms in the bottom of the test tube. 3. A color change occurs. 4. The temperature changes (either increases or decreases). 5. Light is given off – often happens in combustion reactions. 6. A change in smell or taste occurs. Bubbles forming in a reaction Glowing jellyfish: give off light -bioluminescence
Slide # 4 Chemical Reactions Rearrange Atoms Photosynthesis Equation Reactants 6 CO 2 + Products 6 H 2 O + sunlight C 6 H 12 O 6 + carbon dioxide + water glucose 6 O 2 oxygen
Slide # 5 Energy is Conserved in Chemical Reactions 1. Energy is neither created nor destroyed. 2. Energy is transformed from one for into another. 3. The total amount of energy is the same at the beginning of the reaction as at the end of the reaction.
Slide # 6 Energy is Transformed in Chemical Reactions In photosynthesis, light energy is transformed into chemical energy for the plant. Energy is transformed from one form into another.
Slide # 7 Energy and Chemical Reactions 1. Exothermic Reactions: reactions that release energy (energy exits to the environment) – they will heat up! 2. Temperature of surroundings increases b/c energy is released. 3. Examples of exothermic reactions: a. digesting food b. decomposition c. burning fuel 4. Exothermic reactions may give off light A burning match is an exothermic reaction – it gives off light & heat.
Slide #8 Energy and Chemical Reactions 1. Endothermic reactions: absorb energy from the environment 2. Requires energy to form chemical bonds. 3. Energy used may be in the form of light or heat. 4. May (but not always) see a drop in temperature Photosynthesis is an endothermic reaction.
Synthesis 2 or more elements or compounds combine to make one product A + B AB
Decomposition One compound is broken down into 2 or more elements or compounds AB A + B
Single Replacement Replacing of one element in a compound with another element AB + C AC + B
Double Replacement Two compounds exchange elements AB + CD AD + CB
Combustion Fuel burns in the presence of oxygen to produce carbon dioxide and water (along with other by-products) ALWAYS EXOTHERMIC Fuel + O 2 CO 2 + H 2 O
Classify & Balance Each Chemical Equation Warm-Up 1. Mg + O 2 Mg. O 2. H 2 O H 2 + O 2 3. Al + Cu. Cl 2 Al. Cl 3 + Cu 4. Fe. Cl 2 + Na 2 CO 3 Na. Cl + Fe. CO 3
Warm-Up: Check Your Answers: 1. 2 Mg + O 2 2 Mg. O A. Synthesis 2. 2 H 2 O 2 H 2 + O 2 B. Decomposition 3. 2 Al + 3 Cu. Cl 2 2 Al. Cl 3 + 3 Cu 4. Fe. Cl 2 + Na 2 CO 3 2 Na. Cl + Fe. CO 3 C. Single replacement D. Double replacement
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