C3 Chapter 3 Energy of reactions 4.0 / 5 based on 1 rating ? ChemistryEnergy of reactions/Exothermic and endothermic reactionsGCSEAQA Created by: ColdAsteroidCreated on: 07-01-16 18:44 How is energy transferred in an exothermic reaction? Give an example. Energy is released. eg/ combustion 1 of 34 How do we know that it is an exothermic reaction? The temperature of the surroundings increase. 2 of 34 How is energy transferred in an endothermic reaction? Give an example. Energy is taken in. eg/ thermal decompostion, photosynthesis 3 of 34 What is activation energy? The energy needed for the reaction to take place. 4 of 34 What do energy level diagrams do? Shows energy-reactants+products. Whether its endo/exo 5 of 34 On an energy level diagram, how do we know what the activation energy is? Top of curve, difference of reactants and top of curve 6 of 34 How do we know what the energy taken in or released is? The difference between the reactants and the products 7 of 34 HOW do catalysts increase the rate of reaction? A different pathway. Lowers activation energy needed. 8 of 34 How do we find the energy released from burning fuels? (equation) Q=mcΔT= mass x SHC x rise in temp. (water) 9 of 34 What is normally the SHC of water? 4.2J/g/oC 10 of 34 How do we find the energy released per gram of fuel? Divide by amount of fuel burned 11 of 34 Why is a calorimeter used? Metal is conductive => Heat passes into water easier 12 of 34 Why should we stir the water? For even heat distribution. 13 of 34 Why is the energy measured always less than the energy of the fuel? A lot of heat escapes into surroundings rather than the water 14 of 34 What do we get if we react lithium with water? Lithium hydroxide+hydrogen 15 of 34 Why is a polystyrene cup used? Reduces heat escaping-Insulator-More accurate results 16 of 34 What is the vital part of the experiment? Measure start temp. and end temp. of water for difference. 17 of 34 What do we get if we react sodium hydroxide with hydrochloric acid? Sodium chloride and water 18 of 34 How can we improve the experiment? Use a lid, stir the reaction for even heat distribution 19 of 34 In an exothermic reaction, are energy changes shown to be positive or negative? Negative. Energy transferred to other chemicals 20 of 34 In an endothermic reaction, are energy changes shown to be positive or negative? Positive. Energy is gained. 21 of 34 Does breaking bonds require energy or does it release energy? Requires energy (endo) 22 of 34 Does making bonds require energy or does it release energy? Releases energy (exo) 23 of 34 How do the reactants react to make a new compound in terms of bond energies? The bonds are broken, bonds are made for the new product/s 24 of 34 How do we find out whether it's an exothermic/endothermic reaction? "Bond breaking energy" minus the "bond making energy" 25 of 34 How can hydrogen be used as a fuel to power vehicles? Burn in a combustion engine or use in a fuel cell. 26 of 34 What is the hydrogen burnt in to use as a fuel for cars? Oxygen 27 of 34 Is the reaction exo/endothemic between hydrogen and oxygen? exothermic. releases energy when reacted 28 of 34 What type of energy is produced from hydrogen? Electrical 29 of 34 What are the advantages of burning H2 in vehicles? Combines with oxygen in the air; forms just WATER. Very clean 30 of 34 What are the disadvantages with burning H2 in vehicles? Expensive engine, energy from other source needed, explosive 31 of 34 What does a fuel cell need? Fuel+oxygen 32 of 34 How does it gain energy and make electricity? Uses the energy from the reaction to generate electricity. 33 of 34 How do we carry out the experiment? Calorimeter, water temp., spirit temp., stir, flame out, temps. 34 of 34
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