Energy in chemical reaction

• Exothermic


  Chemical reactions that give out heat to the environment
• Endothermic


  Chemical reactions that take in heat from the environment
• Energy profile diagram


  Diagram that shows the amount of energy the chemicals reacting together have (the reactants), the amount of energy needed to start the reaction (the activation energy), and the amount of energy the substances formed during the reaction have (the products)
• Activation energy


  The amount of energy needed to start the reaction
• A change in temperature is one of the signs that a chemical reaction has taken place
• Exothermic reactions


  • Temperature increases during the reaction, heat energy is being given out
• Examples of exothermic reactions

  • Coal burning to heat a room
  • Fireworks exploding
• Endothermic reactions


  • Temperature decreases during the reaction, heat energy is being taken in
• Examples of endothermic reactions


  • Ice melting
  • Using a cold pack to reduce swelling
• When temperature increases during a reaction, it means heat energy is being given out
• When temperature decreases during a reaction, it means heat energy is being taken in
• Ice melting to form water is an endothermic reaction
• Lighting a match is an exothermic reaction
• Steam condensing to form water is an exothermic reaction
• Food cooking is an endothermic reaction
• A plant producing food by photosynthesis is an endothermic reaction
• Getting energy from food (respiration) is an exothermic reaction
• Using a hot pack to relieve back pain is an exothermic reaction
• How to test if a reaction is exothermic or endothermic

  Place a thermometer close to the side of the reaction flask and note if there is an increase or decrease in temperature
• Energy profile diagram


  • Shows the amount of energy the chemicals reacting together have (the reactants), the amount of energy needed to start the reaction (the activation energy), and the amount of energy the substances formed during the reaction have (the products)
• The temperature of the surroundings will increase as energy exits the reaction
• The reaction shown in Fig. 23.8 is exothermic, as the reactants have higher energy than the products