Energy And Chemical Reactions

Question 1

Definition of exothermic reaction

Answer 1

Give out energy to their surroundings 
So bonds can be made 
This means the temperature increases
Delta h is negative 
E.g. Combustion reactions

Question 2

Definition of endothermic reaction

Answer 2

Take in energy
So bonds can be broken
Decrease in temperature
Delta h is positive

Question 3

Enthalpy profile for endothermic reaction

Answer 3

Energy

        /--,--\ products
         |        ---.--
React| 
Ants.|
         |              .= Delta h.   
------,            .                                                            Reaction progress.  ,=activation energy

Question 4

Enthalpy profile for exothermic reaction

Answer 4

Energy
Re  /--.--\
----    .,
               |
               |    .=activatione 
               | products.   ,=delta h
            ,    ---------
Reaction time

Question 5

Delta h equation (change in energy )

Answer 5

E=mc/\t

Energy =massxspecific heat capacityxchange in temperature

Question 6

Bond delta h equation

Answer 6

Bb-bf

Bonds broken -bonds formed

Question 7

What is a fuel cell

Answer 7

It’s something that coverts chemical energy to electrical energy
It converts the energy released by the combustion of a fuel directly in electrical energy

Question 8

Advantages of fuel cells

Answer 8

Doesn’t need to be recharged
Doesn’t create any pollutants
H2o only product h2 is renewable no co2

Question 9

Disadvantages of fuel cells

Answer 9

Hydrogen is highly flammable

Hydrogen is difficult to store

Question 10

What is oxidised and what is reduced in a fuel cell reaction

Answer 10

Hydrogen is oxidised and oxygen is reduced

Question 11

Equation of fuel cell

Answer 11

2h2+o2—>2h2o

Question 12

What is used for the fuel cells electrolyte

Answer 12

Acids or alkalis

Question 13

Two main uses of fuel cells

Answer 13

Cars and spacecrafts

Question 14

Advantages of a fuel cell car

Answer 14

Not rechargeable 
Larger range(good for long distance driving)
Both electrical and fuel cell cars have low emissions of green house gases

Question 15

Disadvantages of fuel cell car

Answer 15

High cost of platinum catalysts for fuel cells
Hydrogen is highly flammable
Hydrogen is difficult to store

Question 16

Electrical car disadvantages

Answer 16

It’s rechargeable
Meaning it’s better for shorter distance driving (smaller range)
Batteries are heavy and expensive

Question 17

Half equation of hydrogen

Answer 17

H2—>2h2++2e-

Hydrogen is oxidised because it’s at the negative electrode where it loses electrons

Question 18

Half equation for oxygen

Answer 18

O2+4h++4e- —>2h2o

Oxygen is reduced because it’s at the positive electrode where it gains electrons

Question 19

Fuel cells info

Answer 19

Fed with oxygen and hydrog to produce water
Hydrogen goes to neg electrode where it’s oxidised
Oxygen goes to pos electrode where it’s reduced
The oxygen reacts to hydroxide ions and hydrogen reacts with hydroxide ions to form water

Question 20

Example of random error

Answer 20

Not measuring water properly

Question 21

Systematic error

Answer 21

Forgetting to keep the lid on

Question 22

Half equation for first stage of rusting

Answer 22

O2+2h2o+4e->4OH-