energy changes and equilibria

Question 1

energy produced by fuels experiment

Answer 1

1) measure 50 cm(3) of water into the beaker
2) set up can, stand and thermometer and one spirit burner, with clock ready
3) light the spirit burner. start the stop clock. take the temp
4) wait exactly 2 minutes
5) put out the flame and take the temperature
- repeat

Question 2

energy produced by fuels

Answer 2

• a calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree
• one calorie is 4.2 joules
• energy changes in chemical reactions can be found by using a bomb calorimeter
• the reactants are mixed in an insoluble container and the temperature change is measured

Question 3

experimental values

Answer 3

• step 1: calculate the energy gained by water (q)
  q= mc change in T

energy gained in water = mass of water * 4.2 * change in temperature

step 2: divide q by the mass of the alcohol used to find out the energy gained by the water per gram of alcohol

step 3: divide q by the numer of moles of the alcohol used to find out the energy gained by the water per mole

energy gained per mole= q/ moles of alcohol burned

Question 4

energy level diagrams

Answer 4

• if the arrow goes down the temp change is negative

- if the arrow goes up then the temp change is positive

Question 5

chemical reaction

Answer 5

• ## during a chemical reaction, energy must be supplied to break bonds whiile energy is released when bonds are formed

Question 6

exothermic reaction

Answer 6

• ## the energy released fro forming new bonds is greater than te energy needed to break existing bonds

Question 7

endothermic reaction

Answer 7

• ## the energy needed to break existing bonds is greater than the energy released fro forming new bonds

Question 8

hydrogen

Answer 8

hydrogen can be burned as a fuel in combustion engines or can be used in fuel cells that produce electricity to power vehicles

Question 9

catalysts

Answer 9

provide a different pathway for a chemical reaction that has a lower activation energy

Question 10

reversible reactions

Answer 10

• if it is exothermic in one direction, it is endothermic in the opposite direction
• the same amount of energy is transferred in each case
• when a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in eac direction

Question 11

haber process

Answer 11

• the raw materials for the haber process are nitrogen and hydrogen
• nitrogen is obtained from the air and hydrogen maybe obtained from natural gas
• the purified gases are passed over a catalyst of iron at a high temperature (about 450) and a high pressure ( about 200 atm)
• some of the hydrogen and nitrogen and nitrogen reacts to form ammonia
• the reaction is reversible so ammonia breaks dwon again into nitroggen and hydrogen
• on cooling, the ammonia liquifies and is removed
• the remaining hydrogen and nitrogen are recycled
• high temp the process would be quicker
• low pressure to compromise between costs and yield

Question 12

conditions of the reaction for equilibria

Answer 12

• if the temperature is raised :
• the yield from the endothermic reaction decreases
• the yield from the exothermic reaction decreased
• if the temperature is lowered:
• the yield from tthe endothermic reaction decreases
• the yield from the exothermic reaction increases

Question 13

gaseous reactions

Answer 13

• an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equattion for that reaction
• a decrease in pressure will favour the reaction that produces the greatest number of molecules sown by the symbol equattion for that reaction