# Chemistry 3

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• Created by: kelz0209
• Created on: 26-04-14 10:49
Describe the type of energy change that happens when new chemical bonds form.
Energy is given out- it's exothermic.
1 of 8
What is the effect of a catalyst on the activation energy of a reaction?
A catalyst lowers the activation energy(by providing a different pathway for the reaction).
2 of 8
Explain how hydrogen fuel cells produce energy.
A hydrogen fuel cell uses the reaction between hydrogen and oxygen which makes water. The reaction is exothermic so energy is given out.
3 of 8
When methane burns in air it produces carbon dioxide and water. The bond energies (kJ/mol): C-H 414 O=O 494 C=O 800 O-H 459. Which two types of bonds are broken during the reaction?
C-H and O=O
4 of 8
Calculate an energy value (in kJ/mol) for: (i) the total bonds broken (ii) the total bonds formed (iii) the difference between the bonds formed and the bonds broken.
(i) (4 x 414) + (2 x 494) = 2644 kJ/mol (ii) (2 x 800) + (4 x 459) = 3436 kJ/mol (iii) 3436-2644 = 792 kJ/mol.
5 of 8
Use the values from the previous question to explain why the reaction is exothermic.
The energy released when the new bonds are formed is greater than the energy needed to break the original bonds, so overall energy is given out.
6 of 8
Amount of energy compared-two different fuels.1g each fuel-burned+heat produced to increase temp of 100cm water.Temperature rise-fuel A=21 +fuel B=32 .(Specific heat capacity of water=4.2 J/g/K.Why is the same volume of water used each time?
E.g. so that the temperature rise is proportional to the amount of heat produced.
7 of 8
Calculate the heat energy transferred to the water from Fuel A, if the water weighs 100g.
100 x 4.2 x 21 = 8820 J/8.82 kJ
8 of 8

## Other cards in this set

### Card 2

#### Front

What is the effect of a catalyst on the activation energy of a reaction?

#### Back

A catalyst lowers the activation energy(by providing a different pathway for the reaction).

### Card 3

#### Front

Explain how hydrogen fuel cells produce energy.

### Card 4

#### Front

When methane burns in air it produces carbon dioxide and water. The bond energies (kJ/mol): C-H 414 O=O 494 C=O 800 O-H 459. Which two types of bonds are broken during the reaction?

### Card 5

#### Front

Calculate an energy value (in kJ/mol) for: (i) the total bonds broken (ii) the total bonds formed (iii) the difference between the bonds formed and the bonds broken.