C5- Energy changes Flashcards

1
Q
  • what happens to energy in chemical reactions
A
  • Energy is conserved
  • the amount of the energy in the universe at the start of the reaction is equal to the amount at the start of the reaction
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2
Q

What must happen for a reaction to transfer energy to surroundings

A
  • the product molecules mss have less energy than the reactants
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3
Q

What does the conservation of energy mean

A
  • the amount of energy in the universe never changes
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4
Q

What is an exothermic reaction

A
  • one that transfers energy to the surroundings usually by heating - temperature around increases
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5
Q

What are examples of exothermic reactions and how do we use them everyday

A
  • Exothermic reactions include combustion, oxidation and neutralisation
  • Everyday uses include self heating cans and hand warmers
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6
Q

What is an endothermic reaction

A
  • A reaction that takes energy from surroundings

- temperature of surroundings will decrease

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7
Q

What are the examples and everyday examples of exothermic reactions

A
  • Thermal decomposition and reaction of citric acid and sodium hydrogen carbonate
  • sport injury pack are based on exothermic reactions
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8
Q

How cam energy transfer be measured- practical

A
  • take the temperature of the reagents - mix them in a polystyrene cup and measure to temperature at the end
  • Loss of energy to surroundings
  • can also measure the effect that variables have on energy transfer e.g concentration
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9
Q
  • What are reaction profiles
A
  • Diagrams that show the relative energies of reactants and products in a reaction and how energy changes over course of a reaction
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10
Q

What is activation energy

A
  • Chemical reactions can only occur when reacting particles collide with each other with sufficient energy. the minimum energy that particles must have to react is called activation energy
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11
Q

What does a reaction profile look like in an exothermic reaction

A
  • Products at l;over energy than reactants

- Difference in height represents energy change in reaction per mole

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12
Q

What does a reaction profile look like for an endothermic reaction

A
  • Products are at a higher energy than the reactants

- Difference is height represents the overall energy change during the reaction in moles

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13
Q

What does the difference in height represent in reaction profiles

A
  • The overall energy change during the reaction per mole
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14
Q
  • How do bonds relate to energy during a reaction
A
  • Energy must be supplied to brea bonds in the reactants

- Energy is related when bonds in products are formed

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15
Q

What happens in exothermic reactions regarding bond breaking

A
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16
Q

What happens in endothermic reactions regarding bind breaking

A
  • The energy needed to break existing bonds is greater than the energy released from forming new bonds
17
Q

What type of reactions are bond breaking and making

A
  • Bond breaking - endothermic

- bond forming- exothermic

18
Q

What is the overall energy change in a reaction

A
  • The difference between the sum of energy needed to break bonds and energy released when bonds are formed is overall energy change
  • Difference between energy to break bonds and energy in formation of bonds
19
Q

Hood you calculate the energy change in a reaction

A
  • Find energy required to break original bonds
  • Find energy released by forming new bonds
  • Find overall energy change for reaction using this equation -
  • Overall energy change = Energy required to break bonds- energy released by forming bonds
20
Q

What is bond energy

A
  • The amount of energy in a bond and thus the amount needed to break it