Endothermic and Exothermic Reactions PDF

Endothermic and Exothermic Reactions  Enthalpy Enthalpy (H) is the measure of heat energy The change in enthalpy (ΔH) tells us how much energy is required or released in during a reaction ΔH = Hproducts – Hreactants Positive ΔH = energy is absorbed Negative ΔH = en...

Endothermic and Exothermic Reactions  Enthalpy Enthalpy (H) is the measure of heat energy The change in enthalpy (ΔH) tells us how much energy is required or released in during a reaction ΔH = Hproducts – Hreactants Positive ΔH = energy is absorbed Negative ΔH = energy is released  Endothermic Reaction Heat (energy) is absorbed into the reaction. The reaction feels cold, temperature decreases The products have more energy than the reactants. ΔH is positive  Exothermic Reaction Heat (energy) is released from the reaction. The reaction feels hot, temperature increases The reactants have more energy than the products. ΔH is negative  Collision Theory States that two atoms, ions, or molecules will react to form products when they collide IF they have enough energy!!! This energy is called the ACTIVATION ENERGY. It is the minimum energy that colliding particles must have in order to react.  Let’s consider the reaction between hydrogen and oxygen to form water: 2H2 + O2 🡪 2H2O + 🡪  Activated Complex - An unstable arrangement of atoms forms momentarily at the activation-energy barrier. Also called TRANSITION Energy 🡪 Reactants STATE. Products Time 🡪  Endothermic or Exothermic??? Activated Complex Activation Energy Energy 🡪 Reactants Heat of Reaction (ΔH) Products Time 🡪  Now let’s look at an endothermic reaction. –What will have higher energy, the reactants or the products? –Will the Heat of Reaction (ΔH) be positive or negative?  Endothermic or Exothermic??? Activated Complex Activation Energy Energy 🡪 Products Heat of Reaction (ΔH) Reactants Time 🡪  Catalyst A CATALYST increases the rate of reaction by lowering the activation-energy barrier.  Does a catalyst affect the Heat of Reaction? Activation Energy without catalyst Activation Energy with catalyst Energy 🡪 Reactants Heat of Reaction (ΔH) Products Time 🡪  Catalyst Decrease the magnitude of the activation energy. Does not change the amount of energy released in the reaction. Converts reactants more rapidly to products.