TOPIC 3 - Chemistry ( Elements of the Sea)

Define exothermic reaction:

In an exothermic change energy is transferred from the system (chemicals) to the surroundings. The products have less energy than the reactants

Define endothermic reaction:

In an endothermic change, energy is transferred from the surroundings to the system (chemicals). They require an input of heat energy - The products have more energy than the reactants

Define activation energy:

The minimum energy required for particles need to collide and start the reaction

Define standard enthalpy change of formation:

The enthalpy change when 1 mole of a compound is formed from its constituent elements in their standard states under standard conditions - 100 kPa and 298K

Define the standard enthalpy of combustion:

The enthalpy change when 1 mole of a compound is burned completely in excess oxygen under standard conditions - 100kPa and 298K

Define the standard enthalpy of neutralisation:

The enthalpy change when solutions of an acid and alkali react to form 1 mol of water under standard conditions 100 kPa and 298K

Why is incomplete combustion different to complete combustion?

Incomplete combustion will lead to soot (carbon), carbon monoxide and water. It will be less exothermic than complete combustion

Method for the acid base titration practical:

1. Pour approximately 100cm3 of the standard solution of known concentration into a beaker.

2. Fill the burette with the standard solution of known concentration

3. Pour approximately 100cm3 of the solution with unknown concentration into a second beake

4. Using a pipette filler and pipette to transfer exactly 25cm3 of solution into a 250cm3 conical flask

5. Add two to three drops of phenolphthalein indicator to the solution in the conical flask and note the initial colour of the indicato

6. Record the initial burette reading

7. Titrate the contents of the conical flask by adding solution to it from the burette until the indicator undergoes a definite, permanent colour change. Record the final burette reading in your table of results. Calculate the titre volume (change in volume in the burette

8. Repeat, calculate and record the volume of solution used in the titration in a table (titre volume). Repeat until two concordant results are obtained. Record all of the results that you obtain

Describe the practical for the enthalpy change of combustion:

1) Use a measuring cylinder to transfer 100cm3 of water into the copper can which is inside the draught shield of the calorimeter

2) Add the lid, stirrer and thermometer

3) Place the calorimeter over and ethanol spirit burner and check that copper can will not extinguish the the flame

4) Accurately weight the spirit burner with the lid on

5)Accurately record the temperature of the water in the copper can

6) Light the spirit burner and, as quickly as possible place inside draught shield underneath the copper can

7) monitor the water temperature and stir regularly whilst spirit burner heats the water

8) When the temp has risen by at least 15 degrees remove spirit burner and extinguish flame by replacing cap

9) keep monitoring water temp and accurately record the highest temperature reached

10) Reweigh the spirit burner with the lid on

Describe the practical of the enthalpy change of neutralisation:

• Measure 25 cm³ of 1 mol dm⁻³ HCl and pour into a polystyrene cup.

• Measure and record the initial temperature of the acid.

• Measure 25 cm³ of 1 mol dm⁻³ NaOH and record its temperature.

• Add the alkali to the acid in the cup and stir gently.

• Record the maximum temperature reached.

• Repeat the experiment at least twice and calculate an average temperature change (ΔT).

How would calculate for enthalpy change of neutralisation?: remember the equation.

List the equation that links moles, concentration and volume:

n = c x v

List the 3 avogadro gas laws:

c1v1=c2v2, V1/n1=V2/n2, V = mol x 24dm3

What is the oxidation state for pure elements?:

0 for all

What about oxidation states and reducing and oxidizing agents?

Oxidized- reducing agent

Reduced- oxidizing agent

What happens to the reactivity of group 7 halogens as you go down the group? + oxidising agent

Reactivity decreases— from a very oxidising agent to a least oxidising agent

Explain what is meant by oxidising agent:

A substance in a redox reaction that gains electrons from another substance, causing the other substance to be oxidized while the agent itself is reduced

Explain what is meant by reducing agent:

A substance in a redox reaction that donates electrons to another species, causing that species to be reduced

What is used as oxidising agents?

Group 7 = Halogens

What is used as reducing agents?

Group 7 = Halide ions

What type of solvent is cyclohexane?

Non-polar organic solvent

Colour of the halogens + their states at room temperature:

Chlorine: Pale green = gas

Bromine: Orange = liquid

Iodine: Brown = solid

How does a redox reaction work?

A more reactive halogen will take the place of the less reactive halide ion. E.g. NaBr + Cl2 —> NaCl + Br2

In a reaction - chlorine water and when the compound is added (NaBr) the chlorine will displace the bromine and then the solution will turn orange (meaning the bromide has been oxidised)