C5 Energy Changes

Question 1

<p>What is an <b>Exothermic</b> reaction?</p>

Answer 1

<p>An exothermic reaction is a reaction that transfers energy to the surroundings</p>

Question 2

<p>What are some examples of exothermic reactions?</p>

Answer 2

<ul><li>Combustion reactions</li><li>Oxidation reactions</li><li>Most neutralisation reactions</li><li>Respiration</li></ul>

Question 3

<p>What happens to the temperature of the surroundings during an exothermic reaction?</p>

Answer 3

<p>The temperature of the surroundings increase during an exothermic reaction</p>

Question 4

<p>What is an <b>Endothermic</b> reaction?</p>

Answer 4

<p>An endothermic reaction is a reaction where energy is transferred from the surroundings</p>

Question 5

<p>What happens to the temperature of the surroundings during an endothermic reaction?</p>

Answer 5

<p>he temperature of the surroundings decrease during an endothermic reaction</p>

Question 6

<p>State a use of endothermic reactions</p>

Answer 6

<ul><li>Instant cooling ice packs</li></ul>

Question 7

<p>State two uses of exothermic reactions</p>

Answer 7

<ul><li>Self-heating cans</li><li>Hand warmers</li></ul>

Question 8

<p>What is a reaction profile?</p>

Answer 8

<p>A reaction profile is a diagram that shows whether the reactants have more or less energy than the products and the overall energy change of a reaction</p>

Question 9

<p>What is <b>activation energy</b>?</p>

Answer 9

<p>Activation energy is the energy required to break bonds to start a reaction</p>

Question 10

<p>Why does a reaction profile always go up at the start?</p>

Answer 10

<p>The reaction always starts with bonds being broken</p>

Question 11

<p>Why does a reaction profile always go down at the end?</p>

Answer 11

<p>The reaction always ends with bonds being made</p>

Question 12

<p>How can you tell if a reaction is exothermic?</p>

Answer 12

<p>If the reactants have more energy than the products, an exothermic reaction has taken place</p>

Question 13

<p>How can you tell if a reaction is endothermic?</p>

Answer 13

<p>If the reactants have less energy than the products, then an endothermic reaction has taken place</p>

Question 14

<p>What type of reaction makes bonds?</p>

Answer 14

<p>Exothermic. Energy is released when chemical bonds are formed</p>

Question 15

<p>What type of reaction breaks bonds?</p>

Answer 15

<p>Endothermic. Chemical bonds are strong so energy needs to be put in to break them</p>

Question 16

<p>How do you work out the overall energy change of a reaction?</p>

Answer 16

<p>Work out the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products</p>

Question 17

<p>How do you work out the energy change from a reaction profile?</p>

Answer 17

<p>Calculate the difference between the energy of the reactants and the energy of the products</p>

Question 18

<p>How do you work out the activation energy from a reaction profile?</p>

Answer 18

<p>The difference between the energy of the reactants and the peak of the profile</p>

Question 19

<p>What is <b>bond energy</b>?</p>

Answer 19

<p>Bond energy is the amount of energy required to break a particular type of bond</p>

Question 20

<p>What is a <b>Chemical Cell</b>?</p>

Answer 20

<p>A chemical cell is a unit that contains chemicals which produce electricity through a reaction</p>

Question 21

<p>What are the main components of a cell?</p>

Answer 21

<p>An Anode &amp; Cathode (made of two different metals) and an electrolyte</p>

Question 22

<p>What is an <b>electrolyte<b>?</b></b></p>

Answer 22

<p>An electrolyte is a solution containing ions</p>

Question 23

<p>What does the voltage of cell depend on?</p>

Answer 23

<p>The type of electrode and the electrolyte</p>

Question 24

<p>What is a <b>battery</b>?</p>

Answer 24

<p>Two or more cells connected in series</p>

Question 25

<p>What happens to the electrodes over time in a chemical cell?</p>

Answer 25

<p>The more reactive metal is used up and the less reactive metal increases in size</p>

Question 26

<p>Why do the chemical reactions stop over time in non-rechargeable cells?</p>

Answer 26

<p>One of the reactants becomes used up</p>

Question 27

<p>How can certain cells be recharged?</p>

Answer 27

<p>By applying an extrenal electrical current which reverses the reactions that took place</p>

Question 28

<p>How does the reactivity of the metal electrodes affect the size of voltage?</p>

Answer 28

<p>The greater the difference between the two metals in reactivity, the greater the voltage</p>

Question 29

<p>Which direction do the electrons move in a cell?</p>

Answer 29

<p>The electrons move from the more reactive metals to the less reactive metal</p>

Question 30

<p>What is a <b>fuel cell</b>?</p>

Answer 30

<p>A fuel cell is a cell which uses a fuel and oxygen (or air) in order to generate electricity</p>

Question 31

<p>What are the products of a hydrogen fuel cell?</p>

Answer 31

<p>Water</p>

Question 32

<p>What are the advantages of Hydrogen fuel cells?</p>

Answer 32

<ul><li>No Pollution (only product is water)</li><li>3 times more powerful than petrol (efficient)</li><li>They burn without reimitting harmful gases</li><li>High energy production</li><li>Reliable</li></ul>

Question 33

<p>What are the disadvantages of Hydrogen fuel cells?</p>

Answer 33

<ul><li>Hydrogen is highly flammable</li><li>Hydrogen needs to be seperated from oxygen which needs fossil fuels</li><li>Hydrogen is difficult to store</li></ul>

Question 34

<p>What reaction happens at the negative electrode of a Hydrogen Fuel cell?</p>

Answer 34

<p>H₂ → 2H +2e^-</p>

Question 35

<p>What reaction happens at the positive electrode of a Hydrogen Fuel cell?</p>

Answer 35

<p>O₂ + 4H^- → 2H²O</p>

Question 36

<p>How do catalysts increase reaction rates?</p>

Answer 36

<p>Catalysts can increase reaction rates by lowering the activation energy, which increases the likelihood of successful collisions</p>

Question 37

<p>How can you tell if a reaction is Exothermic?</p>

Answer 37

<p>Energy released by making bonds > energy required to break bonds
overall energy change of reaction < 0</p>

Question 38

<p>How can you tell if a reaction is Endothermic?</p>

Answer 38

<p>Energy released by making bonds < energy required to break bonds
i.e. overall energy change of reaction > 0</p>

Question 39

<p>Is bond breaking endothermic or exothermic?</p>

Answer 39

<p>Bond breaking requires energy and is therefore Endothermic</p>

Question 40

<p>Is bond making endothermic or exothermic</p>

Answer 40

<p>Bond making releases energy and is therefore Exothermic</p>

Question 41

<p>How do you increase the Voltage output of a cell?</p>

Answer 41

<ul><li>Changing the electrolyte<ul><li>Changing the electrolye changes the reactions that happen at the electrode</li></ul></li><li>Type of Electrode<ul><li>A greater difference in reactivity between the two electrodes will result in the cell having a greater voltage</li></ul></li></ul>

Question 42

<p>How do you calculate the voltage of a battery?</p>

Answer 42

<p>The voltage of the battery is calculated as the sum of the voltage of the individual cells</p>

Question 43

<p>What happens when the chemicals of a cell runs out?</p>

Answer 43

<p>The chemical reactions stop and therefore, the battery no longer works</p>

Question 44

<p>Why can't alkaline batteries be recharged?</p>

Answer 44

<p>In Alkaline batteries, irriversible reactions take place at the electrodes. This means that as soon as one reacting chemical has run out, no more electricity can be produced</p>

Question 45

<p>Why can rechargeable batteries be used multiple times?</p>

Answer 45

<p>In rechargeable batteries, an external electrical current can be applied which reverses the reactions at the electrodes. This means that electricity can continue to be produced as long as an external current can be applied</p>

Question 46

<p>What happens at the anode (negative electrode) in a Hydrogen fuel cell?</p>

Answer 46

<p>Hydrogen is pumped in at the anode. Hydrogen ions are formed as hydrogen molecules are oxidised and lose electrons</p>

Question 47

<p>What is the half equation for the reaction at the anode in a Hydrogen fuel cell?</p>

Answer 47

<p>2H₂ → 4H⁺ + 4e^-</p>

Question 48

<p>What happens at the cathode (positive electrode) in a Hydrogen Fuel Cell?</p>

Answer 48

<p>Oxygen is pumped in at the cathode. Water is formed as the O₂ reacts with the H⁺ ions that have moved through the electrolyte from the anode</p>

Question 49

<p>What is the half equation for the reaction at the cathode in a Hydrogen fuel cell</p>

Answer 49

<p>O₂ + 4H⁺ + 4e^- → 2H₂O</p>

Question 50

<p>What is the overall equation that happens at a hydrogen fuel cell?</p>

Answer 50

<p>2H₂ + O₂ → 2H₂O</p>

Question 51

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Answer 51

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