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KEY CONCEPT Life depends on chemical reactions.

Explore the significance of chemical reactions in life, including the breaking and forming of bonds, release and absorption of energy, and the conservation of matter. Discover the role of activation energy and the difference between exothermic and endothermic reactions.

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KEY CONCEPT Life depends on chemical reactions.

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  1. KEY CONCEPT Life depends on chemical reactions.

  2. Objectives for section 2-4 • Explain the importance of bonds breaking during a chemical reaction • Identify reactions that release or absorb energy.

  3. Bonds break and form during chemical reactions (rxn). • Chemical rxns change substances into different ones by breaking and forming chemical bonds. • Reactants (left) are changed during a chemical reaction. • Products (right) are made by a chemical reaction.

  4. Bond energy is the amount of energy that breaks a bond. • Energy is added to break bonds. • Energy is released when bonds form. • A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3

  5. Chemical reactions release or absorb energy. • Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction. • Examples?

  6. Activation energy is minimum amount of energy needed for reactants to form products

  7. Exothermic reactions release more energy than they absorb. • Reactants have higher bond energies than products. • Excess energy is released by the reaction. • Cellular respiration

  8. Endothermic reactions absorb more energy than they release. • Reactants have lower bond energies than products. • Energy is absorbed by the reaction to make up the difference.

  9. Exothermic or Endothermic?

  10. Quick Quiz Time! • Each question will be worth 2 points • You may NOT talk and/or communicate with a classmate • Scores will be collected and recorded at the end of the chapter

  11. 10. Chemical reactions change substances into different substances by a. conserving matter between the substances. b. breaking and forming chemical bonds c. strengthening electrical charges of substances. d. changing a solvent into a solute.

  12. 11. What is the term for the amount of energy that needs to be added for a chemical reaction to start? a. chemical energy. b. activation energy. c. bond energy. d. reactant energy.

  13. 12. Which phrase best describes an exothermic chemical reaction? a. does not absorb any energy b. forms products with higher bond energy than reactants c. is in a state of equilibrium d. releases more energy than it absorbs

  14. End of Show

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