CHAPTER 4 THERMOCHEMISTRY

EXOTHERMIC  REACTION

-Gives out heat to the surroundings

-Tempareture of the surroundings increases

-Reactants have more energy compared to the products

-Bond formation releases more energy than the energy that required in the bond breaking

ENDOTHERMIC REACTION

-Absorb heat from the surroundings

-Temperature of the surroundings decreases

-Reactants have less energy than the products.

-Bond formation releases less energy than the energy that required in the bond breaking.

Heat of reaction

-is the change in the amount of heat in a chemical reaction

- symbol:         Δ H

-unit: kJ mol^-1

-Standard conditions:

•    Temperature: 25 ̊C / 298 K
•  Pressure: 1 atm
• Concentration of solution:  1.0 mol dm^-3

In an exothermic reaction:

Heat released during the reaction=Heat absorbed by the solution

In an endothermic reaction:

Heat absorbed 

during the reaction   =Heat lost by the solution

For calculation:

Heat change = Heat absorbed or given out 

                         by the aqueous solution

                     = mcθ

Where   m= mass of the solution (in g)

            °C= specific heat capacity of the solution

                    ( in J g^-1̊°C^-1)

              θ= temperature change in the solution ( in °C)

The following are the assumptions made during the calculation of the heat of reaction:

   (a)The solution is dilute. It has the same density as water,which is 1 g cm^-3

   (b)The solution has same specific heat capacity as water,which is 4.2 J g^-1°C^-1

   (c)No heat is lost to or absorbed by the surroundings

e.g.

When 30cm³ of potassium  hydroxide solution is added to 25cm³ nitric acid,the results are as follows.

Initial temperature of potassium hydroside solution =29 ̊°C

Initial temperature of nitric acid= 27  °̊C

Highest temperature of the mixture= 38  °̊C

Calculate the heat change in this reaction.

(density of solution:1 g cm^-3. Specific heat capacity of solution: 4.2 J g^-1  ̊C^-1)

Answer :
Average initial temperature of the solutions=    27+29

                                                                                       2

                                                                      = 28  ̊C             

           ΔH= mcθ

                 = (30 + 25) cm³ (4.2)J g ^-1  ̊C^-1 (38-28) ̊C

                 = 2310 J

                    =2.31 kJ                           

Heat of Precipitation

Heat change when 1 mole of a precipitate is formed from its ions in aqueous solution      

Example of precipitation reaction:

  Pb(NO₃)₂ + K₂SO_{4     --------------->}  PbSO₄ + 2KNO₃

                                                             ΔH = -50kJ mol^-1     

Heat of Displacement

Heat change when one mole of a metal is displaced from its salt solution by a more electropositive metal

Example of displacement reaction:

  Zn + CuSO_{4   --------------------->}     ZnSO₄  +  Cu

                                                             Δ H= -210kJ mol^-1

Heat of neutralization

Heat produced when 1 mole of water is formed from the reaction between an acid and an alkali 

** Complete neutralization of a strong diprotic acid with an alkali produces   

     double amount of heat as compared to a strong monoprotic acid.

e.g. of monoprotic acid: HNO_3,  HCl

            diprotic acid: H₂SO₄

This is because a diprotic acid produces 2 moles of hydrogen ions when it dissociates in water.

H₂SO₄ ----------->   2H⁺ + SO₄^2-

2 moles of hydrogen ions produces 2 moles of water when reacted with    

hydroxide ion from an alkali.

2H⁺ + 2OH^-           ------------> 2H₂O

E.g of neutralization reaction

           HCl + NaOH ----------------->  NaCl + H₂O

                                                              Δ  H = -57.3 kJ mol^-1

           H₂SO₄ + 2NaOH  -----------> Na₂SO₄ + 2H₂O

                                                             Δ  H= -114.6 kJ mol^-1           

Heat of combustion

 Heat produced when one mole of a substance is completely combusted in excess oxygen under standard condition.

E.g        CH₄ + 2O₂ -----------> CO₂ + 2H₂O

                                                                 Δ H=-890 kJ mol^-1

Hope you understand better after watching those videos.!!! Do leave us some comment!

                                                 

 

CHAPTER 5 CHEMICAL FOR CONSUMERS--MEDICINE

1. ANALGESICS

-used to relieve pain without causing numbness or affecting consciousness.

(a)Aspirin

-function: to reduce fever,headache,arthritic pain and dental pain

-not suitable to be used by:

  Children,pregnant women,gastric patient,           
  kidney disease

-correct usage: taken with plenty of water, taken   
 after the food

-Reasons:

  =>aspirin is acidic

  =>will cause ulceration and internal bleeding

  =>reduce irritation of stomach wall

-Side effects:

  =>brain and liver damage

(b) Paracetamol

-neutral

-used to replace aspirin(given to children)

-side effects: liver damage

(c) Codeine

-headache tablets, cough medicine
-side effects

 =>drowsiness

 =>addiction

 =>depression

 =>nausea

 =>dry mouth

2. ANTIBIOTICS

-used to kill or slow down the growth of bacterias

-to treat infections caused by bacterias.

(a)penicillin

-treats:
 =>tuberculosis(TB)

 =>pneumonia

 =>syphilis

 =>gonorrhea

(b)Streptomysin

-treats:

 =>tuberculosis

 =>pneumonia

 =>whopping cough

 * antibiotics are usually given by injection and are not taken orally—because they are broken down by the acid in stomach.

* correct usage:

   The patient should take the full course of the antibiotics.

  -to make sure all the bacterias are killed

  -otherwise,he may become ill again and the bacterias may become more 

   resistant to the antibiotics

  -the antibiotic is no longer effective

  -doctor have to prescribe a different and stronger antibiotics to fight the same

    infection

*side effects

 -headache

-allergic reaction

-diarrhoea

3.PSYCHOTHERAPEUTICS

-used to alter abnormal thinking,feelings, or behaviours

(a) stimulant

-to reduce fatigue and elevate mood

-amphetamine

-side effect: anxiety,hallucination

(b) antidepressant

-reduce tension and anxiety

-e.g Transquilisers

        -causes drowsiness

        Barbiturates

        -causes addiction,kill themselves accidentally by taking overdose

(c) antipsychotic

-to treat psychiatric illness such as schizophrenia

-chlorpromazine

-Side effect: drowsiness

CHAPTER 5 CHEMICAL FOR CONSUMERS--FOOD ADDICTIVES

Natural or synthetic substance which is added to food to prevent spoilage or to improve its appearance, taste or texture.

1. Preservatives

-added to food to slow down or prevent the growth of microorganisms,so that the food can be kept for longer periods of time.

Sodium nitrate

-to preserve and stabilize the red colour in meats.

-causes stomach cancer/ brain damage

Salt

-causes high blood pressure,heart attack,stroke

Sugar

-causes obesity,tooth decay,diabetes

Sulphur dioxide

-fruit juice

-causes asthma,allergies

Benzoic acid/ sodium benzoate

-oyster sauce

2.Antioxidants

-added to food to prevent oxidation that causes rancid fats and brown fruits.

Ascorbic acid(vitamin C)

  =fruit juice

  =to preserve the colour of fruit juice

3.Flavourings

   -Improve the taste of food and restore taste loss due to processing

Sugar,salt,vinegar

Monosodium glutamate(MSG)

-To bring out the flavor in many food.

-causes headache,vomiting and difficulty in breathing

Aspartame

-To sweeten the food.

-200 times sweeter than sugar,but it has fewer calories than sugar

-suitable for diabetic patients and for people who want to loss weight.

Ester

Pentyl ethanoate (banana flavor)

4. Stabilizers

-help to prevent an emulsion from separating out.

-example of food: margarine,butter,ice-cream

-example of stabilizers: lecithin, acacia gum

5. Thickeners

-used to thicken the food.

-e.g : modified starch,pectin,acacia gum,gelatin,agar

6.Dyes

-add or restore the colour in a food in order to enhance its visual appearance and to match customers’ expectations

Azo compounds

-red,orange,yellow

-e.g tartazine(yellow)

         =causes hyperactive,difficult to sleep

Triphenyl compounds

-blue, green

-e.g. Brilliant blue FCF