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1.5.1 Exothermic and Endothermic Reactions
06/03/2023
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1.5.1 Exothermic and Endothermic Reactions ✓ Chemistry MOC Energy Transfer During Exothermic and Endothermic Reactions Whenever there are chemical reactions, there are changes in energy. All chemicals store a certain amount of energy, and some store more than others. Energy is never created or destroyed, so if the products of a reaction contain a different amount of energy to the reactants, then energy has either been taken in from or transferred to the surroundings Exothermic Reactions An exothermic reaction <-> a reaction which transfers energy to the surroundings Exothermic reactions are usually shown by a rise in temperature. There are many different types of reaction that are usually exothermic: Burning fuels ● Neutralisation reactions Many oxidation reactions ● Required practical We can measure energy transfer by taking the temperature of reagents, putting them in an insulated environment, reacting them, and measuring the temperature at the end of the reaction. This tells us whether a reaction is endothermic or exothermic ● • Exothermic reactions are used in everyday life to heat things up. For example, in a hand warmer or a heating system HEAT ● HEAT 800.000 。。 HOTTER THAN SURROUNDINGS HEAT HEAT EXOTHERMIC Endothermic Reactions An endothermic reaction <-> a reaction which takes in energy from the surroundings Endothermic reactions are much less common than exothermic ones. They can be shown by a decrease in temperature. Here are some examples of endothermic reactions: The reaction between citric acid...
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Alternative transcript:
and sodium hydrogencarbonate... • Thermal decomposition • Endothermic reactions can also be used in everyday life. For example, in ice packs that can instantly become cooler without a freezer HEAT COOLER THAN SURROUNDINGS HEAT HEAT ENDOTHERMIC HEAT Reaction Profiles Reaction profiles show the relative energies of the reactants and products in a reaction, and how energy changes in a reaction. The energy of the reactants and products is shown on the y-axis, and the reaction progress on the x. The arrows will show whether a reaction is exothermic (downwards) or endothermic (upwards), Activation energy is shown as the initial rise in energy in a reaction and is the minimum amount of energy needed for the reactants to collide with each other and start the reaction. ENERGY EXOTHERMIC REACTANTS ● ENERGY IS RELEASED PRODUCTS PROGRESS OF REACTION ENERGY Copyright © Save My Exams. All Rights Reserved save my exams ENDOTHERMIC PRODUCTS ENERGY IS ABSORBED T REACTANTS PROGRESS REACTION • In an exothermic reaction, energy is given out, so the energy of the products will be lower than the energy of the reactant and the overall change in energy is negative • In an endothermic reaction, the energy of products is higher than the energy of the reactants because energy is taken in. The overall energy change will be positive The Energy Change of Reactions (HT only) In a chemical reaction, old bonds are broken and new bonds are formed. Bond breaking is an endothermic process; energy must be supplied to break existing bonds Bond forming is an exothermic process; energy is released when new bonds are formed If a reaction is exothermic, this means that the energy released when new bonds are formed is greater than the energy used to break the existing bonds. In an endothermic reaction, the opposite is true. Bond energies Every chemical bond has bond energy associated with it that varies depending on the compound the bond occurs in. Theres known bond energies can be used to calculate the overall energy change for the reaction. Overall energy change -> the sum of the energies needed to break bonds in the reactants minus the energy released when new bonds are formed in the products To calculate the energy change for a reaction: 1. Find the energy required to break the original bonds 2. Find the energy released by forming the new bonds 3. Find the overall energy change by taking away energy to break bonds from energy to form new bonds