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Chemistry C3 > 3.3 Energy calculations > Flashcards

3.3 Energy calculations Flashcards

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1
Q

What is the equation we can use to work out the amount of energy released? (include units)

A

energy released = mass (of substance e.g.water) x specific heat capacity (of substance e.g.water) x rise in temperature
Joules = grams x degrees C x degrees C
( Q=mc^t)

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2
Q

What happens when fuels and food react with oxygen?

A

energy is released in an exothermic reaction

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3
Q

What can a simple calorimeter be used for?

A

can be used to compare the energy released by different fuels or different foods in a school chemistry lab

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4
Q

What examples are there for reactions that can be used with the temperature change energy transfer with a calorimeter technique?

A

neutralisation and displacement reactions

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5
Q

What is the difference between the energy levels of the reactants and the products?

A

the energy change during a reaction

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6
Q

What is the energy change during a reaction measured in?

A

kJ/mol

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7
Q

How can we show the relative difference in energy of the reactants and products?

A

energy level diagrams

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8
Q

Describe the energy level diagram in an exothermic reaction:

A

the energy level of the reactants is higher than that of the products and energy is released in the reaction to the surroundings which get hotter

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9
Q

Describe the energy level diagram in an endothermic reaction:

A

the products are at a higher energy level than the reactants so energy is absorbed from the surroundings in the reaction so they get colder

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10
Q

What is the activation energy?

A

the minimum amount of energy needed to start a reaction (before colliding particles can react)

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11
Q

How can catalysts increase the rate of reaction?

A

provide an alternative pathway to the products which has a lower activation energy
this means that the higher proportion of reactant particles now have the energy to react

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12
Q

What happens when new bonds are formed, what process is it?

A

energy is released

exothermic process

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13
Q

What happens when bonds are broken, what process is it?

A

energy has to be supplied to break chemical bonds and energy is taken in from the surroundings
endothermic process

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14
Q

What is the name of the energy needed to break the bond between two atoms called?

A

the BOND ENERGY for that bond

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15
Q

What are bond energies measured in?

A

kJ/mol

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16
Q

How can we use bond energies?

A

to work out the energy change for many chemical reactions

17
Q

What do we need to work out to calculate the energy change for a chemical reaction?

A
  • how much energy is needed to break the chemical bonds in the reactants
  • then how much energy is released when the new bonds are formed in the products
18
Q

What decides whether a reaction is endothermic or exothermic (considering bonds)?

A

Endothermic: the energy released when new bonds are formed is less than the energy absorbed when bonds are broken
Exothermic: the energy released when new bonds are formed is greater than the energy absorbed when bonds are broken

19
Q

What are the problems with using fossil fuels?

A
  • they are running out
  • releases carbon dioxide which contributes to greenhouse effect (global warming)
  • releases sulfur dioxide and nitrogen oxide which creates acid rain
  • sourcing is not good for environment etc
20
Q

What is much of the world’s pollution caused by?

A

the increasing numbers of vehicles on our roads

21
Q

What is being considered as an alternative fuel and what is its reaction?

A

hydrogen:
hydrogen + oxygen –> water
2H2 + O2 –> 2H2O

22
Q

What are the advantages and disadvantages of hydrogen fuel?

A

Advantages:
- does not produce CO2 which could help tackle global warming

Disadvantages:

  • safety and storage is an issue
  • supplying hydrogen to burn in cars is also an issue… if we use electrolysis then electricity generated from non-renewable fossil fuels doesn’t help the environment
23
Q

What is a more efficient way to use energy from oxidising hydrogen and how does it work?

A

fuel cell:

  • cells fed with hydrogen and oxygen which produce water
  • most of energy released in reaction is transferred to electrical energy (can be used to run vehicle)
  • constant supply required
24
Q

What is the challenge of hydrogen-powered engines?

A

to match the performance, price and convenience petrol or diesel cars whilst being cleaner with great benefits

Chemistry C3 (3 decks)

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