Unit 3 - Energy from Reactions Flashcards Preview

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Flashcards in Unit 3 - Energy from Reactions Deck (27):
1

How can you measure the amount of energy released by a chemical reaction? (in solution)

Taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction

2

What is an exothermic reaction? 

A reaction which gives out energy to the surrounding, usually in the form of heat and usually shown by a rise in temperature

3

What is an endothermic reaction?

One which takes in energy from the surrounding, usually in the form of heat and usually shown by a fall in temperature

4

What happens during a chemical reaction?

Old bonds are broken and new bonds are formed

5

What process is breaking bonds?

Endothermic 

6

What process is bond forming?

Exothermic

7

In an endothermic reaction, what is they energy required to break old bonds?

Greater than the energy released when new bonds are formed

8

In an exothermic reaction what is the energy required for bond formation?

Greater than the energy used in breaking old bonds

9

How is fuel energy calculated?

Using calorimetry

10

How do you measure the amount of energy release when a fuel is burnt?

Burn the fuel and use the flame to heat up some water - this is calorimetry

11

What is the method for calorimetry?

  1. Put 50cm of water in the copper can and record its temperature
  2. Weigh the spirit burner and lid
  3. Put the spirit burner underneath the can, and light the wick. Heat the water, stirring constantly, until the temperature reaches bout 50℃ 
  4. Put out the flame using the burner lid, and measure the final temperature of the water
  5. Weigh the spirit burner and lid again

12

In energy level diagrams: what does an exothermic reaction look like?

The products are at a lower energy than the reactants 

aka 

                   Reactants 

                                   Products 

13

In energy level diagrams: What does the difference in heigh represent in an exothermic reaction?

The energy given out in the reaction (per mole)

14

In energy level diagrams: what does the intial rise represent?

The energy needed to break the old bonds (the activation energy)

15

In energy level diagrams: what do endothermic reactions look like?

The products are at a higher energy than the reactions 

aka

                     Products

                       Reactants 

16

In energy level diagrams: what does the difference in height represent in endothermic reactions?

The energy taken in during the reaction (per mole)

17

What is the activation energy?

The minimum energy needed by reacting particles to break their bonds

 

18

What do catalysts do to activation energy?

lowers it

19

how is the change in activation energy made by a catalyst represented on a energy level diagram?

By the same curve but lower down

20

What do hydrogen and oxygen react together to produce?

Water

21

is the reaction between hydrogen and oxygen endothermic or exothermic?

exothermic (releases energy)

22

Hydrogen gas can be burn in oxygen as a fuel in the..

combustion engines of vehincles

23

Pro's of reacting hydrogen in oxygen in a combustion engine?

Hydrogen combines with oxygen in the air to form just water so its very clean

24

 Cons of reacting hydrogen in oxygen in a combustion engine?

You need a special, expensive engine

Hydrogen is very hard to store safely as its very explosive

25

What is a fuel cell?

An electrical cell that's supplied with a fuel and oxygen and uses energy to form the reaction between them to generate electricity

26

What cell can hydrogen be used in?

A hydrogen-oxygen fuel cell

27

Advantages of fuel cells?

More practical than solar cells

Safer than nuclear power

Don't produce any conventional pollutants

They would eventually help countries to become less indepentant on crude oil