Unit 3 - Energy from Reactions

Question 1

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

Answer 1

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

Question 2

What is an exothermic reaction?

Answer 2

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

Question 3

What is an endothermic reaction?

Answer 3

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

Question 4

What happens during a chemical reaction?

Answer 4

Old bonds are broken and new bonds are formed

Question 5

What process is breaking bonds?

Answer 5

Endothermic

Question 6

What process is bond forming?

Answer 6

Exothermic

Question 7

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

Answer 7

Greater than the energy released when new bonds are formed

Question 8

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

Answer 8

Greater than the energy used in breaking old bonds

Question 9

How is fuel energy calculated?

Answer 9

Using calorimetry

Question 10

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

Answer 10

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

Question 11

What is the method for calorimetry?

Answer 11

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

Question 12

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

Answer 12

The products are at a lower energy than the reactants

aka

Reactants

Products

Question 13

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

Answer 13

The energy given out in the reaction (per mole)

Question 14

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

Answer 14

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

Question 15

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

Answer 15

The products are at a higher energy than the reactions

aka

Products

Reactants

Question 16

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

Answer 16

The energy taken in during the reaction (per mole)

Question 17

What is the activation energy?

Answer 17

The minimum energy needed by reacting particles to break their bonds

Question 18

What do catalysts do to activation energy?

Answer 18

lowers it

Question 19

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

Answer 19

By the same curve but lower down

Question 20

What do hydrogen and oxygen react together to produce?

Answer 20

Water

Question 21

is the reaction between hydrogen and oxygen endothermic or exothermic?

Answer 21

exothermic (releases energy)

Question 22

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

Answer 22

combustion engines of vehincles

Question 23

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

Answer 23

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

Question 24

Cons of reacting hydrogen in oxygen in a combustion engine?

Answer 24

You need a special, expensive engine

Hydrogen is very hard to store safely as its very explosive

Question 25

What is a fuel cell?

Answer 25

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

Question 26

What cell can hydrogen be used in?

Answer 26

A hydrogen-oxygen fuel cell

Question 27

Advantages of fuel cells?

Answer 27

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