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Poppy > Energy Calculations > Flashcards

Energy Calculations Flashcards

1
Q

What is the amount of energy released by by fuels measured in

A

Joules or sometimes calories

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2
Q

What is the conversion rate between calories and joules

A

1 cal: 4.2 J

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3
Q

What is used to measure the amount of energy released when substances burn

A

Calorimeter

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4
Q

What type of reaction occurs when fuels and foods react with oxygen

A

Exothermic

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5
Q

What is the simplest calorimeter and how does it work

A

Some water in atlas beaker of metal can, when the substance burns it heats the water and the rise in temperature depends on the amount of energy released

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6
Q

What is the equation you use to calculate the amount of energy transferred

A

Q=mcΔT
Q is the amount of energy transferred in joules
M is the mass of water in grams
C is the specific heat capacity in water in J/gdegrees
ΔT is the temperature change in degrees

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7
Q

Why do simple calorimeters not give accurate results

A

Because much of it was used to heat the surroundings

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8
Q

How can the results of simple calorimeters be used

A

To compare the energy released by different fuels

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9
Q

What can be used to compare the energy released by burning different fuels

A

The energy change in kj per gram or the energy change in kj per mole can be used

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10
Q

How can the energy change in kj/mol can be calculated

A

By multiplying the energy change in kj/g by the relative formula mass

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11
Q

What happens when a reaction takes place in a solution

A

Energy is transferred to or from the solution

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12
Q

How can you reduce the energy transferred into the surroundings of reactions in solutions

A

In an insulated container

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13
Q

When calculating the temperature change of a solution what do we assume?

A

They behave like water;
1 cm3 of the solution has a mass of 1g
The specific heat capacity of water is 4.2J/gdegrees

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14
Q

What do we assume when we add a solid to water or a solution in order to calculate the energy transferred

A

We assume that the volume of the volume doesn’t change and that 1cm3 has the mass of 1g and that its specific heat capacity is 4.2

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15
Q

What can we use to show the energy changes for chemical reactions

A

Energy level

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16
Q

What does the difference between the energy levels of reactants and products represent

A

The energy change for the reaction

17
Q

What must happen in order for a reaction to happen

A

During a chemical reaction bonds in the reactants must be broken for the reaction to take place

18
Q

What causes energy to be taken in an endothermic reaction

A

Breaking bonds

19
Q

What is the minimum energy required for a reaction to take place called

A

Activation energy

20
Q

Why are a reactions endothermic

A

When new bonds are formed in the products which release energy

21
Q

What is energy needed for in a reaction

A

To break the bonds

22
Q

What is released when new bonds are formed in products

A

Energy is released

23
Q

What makes the overall reaction exothermic or endothermic

A

The difference in these energy changes

24
Q

What is the bond energy

A

The energy needed to break the bond between 2 atoms

25
Q

How can we use the bond energies to calculate the overall energy change

A

An equal amount of energy is released when the bond forms between 2 atoms and so we can use bond energies to calculate the overall energy change for a reaction

26
Q

What are bond energies measured in

A

KJ/mol

27
Q

What steps are required to calculate the energy change for a reaction

A

The total amount of energy needed to break all of the bonds in the reactants
The total amount of energy released in making all of the bonds in the products
The difference between the two totals

28
Q

Why are fossil fuels bad

A

They are non renewable and cause pollution

29
Q

What are the advantages of using hydrogen as a fuel

A

It burns easily and releases a large amount of energy per gram
It produces no carbon dioxide when it is burned, only watwer

30
Q

Where can hydrogen be used

A

In combustion engines

In fuel cells to power vehicles

31
Q

What is the disadvantage of using hydrogen as a fuel

A

It is flammable and not safe

Supply and storage issues

32
Q

What do vehicles that use fuel cells need to match normal cars on

A

Performance, convenience, cost

Poppy (12 decks)

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