Energy and Chemical Reactions

1) Atoms and compounds have potential energy. What kind of potential energy?

2) Your body uses chemical reactions to store energy in muscle and fat. What kind of energy? Are those reactions exothermic or endothermic?

3) Plants store the energy from sunlight in a sugar called glucose. This is a chemical reaction called photosynthesis. Is photosynthesis exothermic or endothermic?

4) Burning a piece of wood is a chemical reaction, and energy is released as heat. What form of energy was it before it was released? Where was it stored?

5) Glucose (C₆H₁₂O₆) is one of your body’s main sources of energy. Your body converts glucose and oxygen into CO₂ and H₂O. (This is why we inhale oxygen and exhale carbon dioxide.) The potential energy of the carbon dioxide and water is less than the potential energy of the glucose and oxygen. Is this an exothermic reaction or an endothermic reaction?

6) As atoms get closer together, their electric potential energy gets less. But if they get too close together, their potential energy starts to increase again. Draw a graph of potential energy versus distance showing this change in energy.

7) In Question 6 I mentioned that potential energy increases if the atoms get too close together. Why does this happen? (Think about that balance of forces in a compound.)

8) Imagine a chemical reaction in water that causes the temperature of the water to decrease. Is this exothermic or endothermic?

9) It always takes energy to break chemical bonds. Is this exothermic or endothermic?

10) What kind of reaction stores energy, exothermic or endothermic?

11) If you light a candle, the wax in the candle reacts with oxygen in the air to make carbon dioxide and water. Is this an endothermic reaction or an exothermic reaction? How can you tell? Where does the activation energy come from?

12) Draw a graph, with energy on the y axis, showing an endothermic chemical reaction. Label the products, reactants, and the activation energy.

13) 2H₂ + O₂ ® 2H₂O + energy. Draw a picture of this reaction, using circles for the atoms, and make sure you consider the difference in potential energies when drawing the circles.

14) And here’s the question that ties together most of what we’ve done with chemistry this year! Sodium reacts with chlorine. The reaction is exothermic. Predict the formula for the product, then write a balanced equation for the reaction. Include “energy” in your equation. Finally, draw a picture for the equation using circles for the electron clouds.