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Information on exothermic and endothermic reactions, their energy changes, and the concept of enthalpy. Students will learn how to identify exothermic and endothermic reactions based on the change in energy and temperature. The document also covers the concept of activation energy and its role in chemical reactions.
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In your own words describe an exothermic reaction You might use these words – energy, enthalpy, temperature, increase, decrease, release, require Are the following reactions exothermic or endothermic? Oxidation of iron to rust Freezing water to form ice Bond making Bond breaking
Energy changes in chemical reactions If a reaction requires energy to occur, we say it is endothermic. This means that the temperature of the surroundings will decrease as the reaction has used up some of the heat energy. If a reaction gives off energy, we say it is exothermic. This means that the temperature of the surroundings will increase as the reaction has given some of the heat energy to the surroundings. Exo Exo Endo Endo Are the following reactions exothermic or endothermic? Water evaporating Metal reacting with acid Forming chemical bonds Breaking chemical bonds
We measure change in energy using a term called enthalpy (H ), measured in J or kJ. This is a measure of how much heat energy a chemical has. Energy changes in chemical reactions are measured by the change in enthalpy that occurs as a reactant forms a product. ΔH = H products
reactants If a reaction releases energy (exothermic) heat is a product If a reaction requires energy (endothermic) heat is a reactant
products
reactants
products
a Ea is activation energy – the energy required to start a reaction off. Can be big or small.
Require energy. Reactants have more/less energy than products. The value for ΔH will be positive/negative.
products
reactants
a
For A:
When we change states we are making and breaking bonds. We can label these processes as exothermic or endothermic reactions. Solid Gas Liquid Liquid Gas Solid Consider the intermolecular bonds. Which side breaks intermolecular bonds? Which side makes intermolecular bonds? Breaking intermolecular bonds Making intermolecular bonds Endothermic Exothermic
When we dissolve ionic compounds we are both making and breaking bonds. This can be an exothermic or endothermic process depending on the strength of the bonds being formed or broken. What bonds are we breaking? What bonds are we forming? Ionic bonds Intermolecular bonds Exothermic reaction Bonds formed release more energy than energy required to break bonds. Product has less energy than reactant. pg (^104) Excess energy is released to surroundings
