C3 = Energy Calculations

Question 1

Give an alternative fuel to fossil fuels, with one advantage and one disadvantage.

Answer 1

Hydrogen

A = Burns easily to power vehicles, no harmful gases released just water.

D = Hard to contain and store, could cause safety issues.

Question 2

Add 25cm3 of nitric acid and 25cm3 of potassium. Temperature rises by 12 degrees. Specific heat capacity is 4.2 J/g oC, what’s the energy change?

Answer 2

2,520 J or 2.52 KJ

Why?

25 add 25 = 50 X 4.2 X 12 = 2520/100 = 2.52 KJ

Question 3

When 5.6g of iron reacted with 200cm3 of copper solution, temperature change 17 degrees. What’s the energy change in kg/mol?

Answer 3

142.8 kg/mol

Reacting with what X specific heat capacity X temp change

200 X 4.2 X 17 = 14,280

Energy change / Ar of reactant

14,280 / 56 = 255

1 mole of energy change X amount of reactant used in the reaction

255 X 5.6 = 1,428

g/mol / 10 = kg/mol

142.8 kg/mol

Question 4

What is specific heat capacity

Answer 4

4.2

Question 5

What’s Ar and Mr

Answer 5

Ar = relative atomic mass (bottom/ biggest number, protons + neutrons)

Mr = relative molecular mass (all the Ar of a compound added)

Question 6

0.5g of fuel burned, heats 200ml of water, temp increased by 14 degrees. What’s the energy released per gram of fuel?

Answer 6

2,352 J/g = 23.52 KJ/g

Why?

200 X 4.2 X 14 = 11,760 J

11,760 / reactant: 0.5 = 2,352 J/g

2,352/100 = 23.52 KJ/g

Question 7

How to convert J into KJ/mole

And

How to convert J into KJ/g

And

How to convert g into Kg

Answer 7

J=KJ/mol : divide by 1000

J=KJ/g : divide by 100

G=kg : divide by 10

Question 8

Titration : 50cm3 of solution was made using 5.6g of potassium oxide, what is its concentration in g/dm3 and mol/dm3 ?

Answer 8

1cm3 = reactant / solution

5.6 / 50 = 0.112

1 dm3 is 1000x bigger = 112g/dm3

1 mole of potassium oxide KOH (39 + 16 + 1) = 56g

To find mole per dm3 just divide g/dm3 by the Mr of the molecule

112/56 = 2

2 moles/dm3

Question 9

What is a titration?

Answer 9

To accurately measure how much acid and alkali are needed in order to react together completely.

Question 10

How do you calculate kg/mol when given energy change?

Answer 10

Energy change X Ar

Question 11

What equation measures energy transfer and the units

Answer 11

Q = m X c X temp change

Q = energy transferred (J) 
M = mass (g) a.k.a.ml)
C = Specific heat capacity (J/goC)
T = Temperature change (oC)

Question 12

Why are there optimum pressures and temperatures

Answer 12

An average is found because higher pressures and lower temperatures would increase yield

BUT

Higher pressures are EXPENSIVE
Lower temps would take a LONG TIME

So a happy medium is found

Question 13

Describe the Haber process

Answer 13

Nitrogen + hydrogen = Ammonia

Iron catalyst
450 degrees
200 a.t.s

15% yield

N2 + 3H2 =REVERSIBLE= 2NH3

Question 14

How do you change the concentration of the reactant or product

Answer 14

The reactant always tries to reach equilibrium so by altering the concentrations more product is formed.

Question 15

What’s equilibrium

Answer 15

When the rate of forward reaction is equal to the rate of reverse reaction

Question 16

Describe an Exothermic energy diagram

Answer 16

Reactants start high
Small kick of activation energy
Products low

Question 17

Describe an endothermic energy diagram

Answer 17

Reactants low
Large kick of activation energy
Products high

Question 18

Describe the effects of a catalyst on any reaction

Answer 18

Lower activation energy needed

Question 19

If you increase temperature, has the reaction been exo/endothermic?

Answer 19

Endothermic

Question 20

What can measure an Exothermic reaction and what does it exactly measure?

Answer 20

Calorimeter

The amount of energy released (J or Calories)

Question 21

What’s the equation for the number of moles

Answer 21

Mass/ relative formula mass

Question 22

Calculate the energy change for burning propane?

C3H8 + 5O2 = 3CO2 + 4H2O

Answer 22

2,054 = Exothermic

How?

1) Draw out all of the bonds in each compound
2) Add the bond energies, if there’s a number before and after X it
3) Second number - first number
4) If it’s positive it’s Exothermic, so endothermic if negative. That’s because if it’s positive there’s extra energy released, if it’s a negative it’s in need of taking in energy from the surroundings so the bonds can be formed.