In chemistry a reaction is a process by which matter changes. We often change matter. W?hat is matter? Anything or any substance that has a mass can be considered as matter. Non matter includes different forms of energy such as heat, light, and electricity. What matter does the picture show? There is a boy , he is wearing a cotton shirt. He is holding a metal spoon. The spoon contains some kind of food. He is inside a room. The room is filled with air.
In chemistry we study three kinds of changes. They can also be described as 'reactions'. They are 1. Physical changes, Chemical changes and Nuclear changes.
Is there a difference between Mixing and Dissolving. Dissolving is a special type of mixing. Dissolving should produce a solution. What is a solution? When you add salt powder to water the solid part disappears in the liquid. SALT + WATER → SALT WATER. That is................... Solute + Solvent → Solution. Dissolving produces a homogeneous product.
Chemical Changes can be represented by equations. Some of the information given by them in this chapter are explained by this diagram. Classifying Chemical Reactions. Chemical changes are vivid and varied. There are many ways of classifying them. Here is a simple way to do that using a basic knowledge of chemistry.
This is an example of burning or combustion. CaO(s) + CO2 (g) = CaCO3(s) Thereaction is slow at low temperature but heating will reverse the reaction. S (s) + O2 (g) = SO2 (g) (Combustion) B:- Chemical decomposition. ![]() Using symbols:- 2H2O(l) = 2H2 (g) + O2 (g) A few other example. 2 KMnO4 (s) = (Heat) K2MnO4 (s) + 2 O2 (g) (A catalyst can speedup) C:- Decomposition yet reversible. Method:-Heat some ammonium chloride in an evaporating dish . Place a funnel as shown What to expect:- N2O4 ↔ 2 NO2 (High temperature shifts to right) WARNING:- Wear tinted safety glass and stand back.
BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) ↧ + 2 NaCl (s) Some other ways of categorising chemical reactions. 1. Acid + Metal reactions. Zn(s) + 2 HCl(aq) → ZnCl2 (aq) + H2 (g) 2. Acid + alkali reactions NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l) 3. Acid + salt reaction. 2 HCl (aq) + CaCO3 (s) → CaCl2 (aq) + H2CO3 H2CO3 (aq) → H2O (l) + CO2(g) 4. Salt + Metal reactions Fe + CuSO4(aq) → FeSO4(aq) + Cu (s) 5. Salt + Salt reactions 2 NaCl(aq) + AgNO3(aq) → AgCl↧ + Na2NO3(aq) 6. Exothermic reactions C6H12O6 + 6 O2= 6 CO2 + 6 H20 + Energy (Respiration reaction) 7. Endothermic reactions 6 CO2 + 6 H20 + light = C6H12O6 + 6 O2 (Photosynthesis) 8. Oxidation and reduction reactions 3 C (s) + 2 Fe2O3(s) = 4 Fe(s) + 3 CO2 (g) Oxidation originally meant combining with oxygen or removal of hydrogen. Now it has been extended to other reactions. A good way to classify them is by examining the transfer of electrons. Donating of electrons is Oxidation while gaining of electrons is Reduction. How to remember. Think of an OIL RIG.
Fig. 7. Reactions in a simple cell producing a current.
Anodic Reaction ...... Oxidation Zn = Zn++ 2 electrons. Zinc ions go into solution. Electrlyte dil. Hydrochloric acid ionises as …... HCl ↔ H+ + Cl- Cathodic reaction ..... Reduction 2H+ + 2 electrons = H2 (g) From question 1. to 6. What type of a reaction is illustrated by the picture shown? A. Physical change. B. Chemical change. C. Nuclear change. D. No change. 1. Using a mixer. 2. Burning magnesium. 3. Magnetizing iron. 4. Pounding yam. 5. Sun producing heat. 6. Mixing baking powder and vinegar. From Q.7 to Q.10. 7. Lylie added some soil into a test tube and stirred well. She observed that the resulting mixture to be cloudy while some settled down as a deposit. What could be her best inference,referring to diagrams 1 and 2. A. Soil is soluble in water B. Soil is not soluble in water. C. A chemical change has taken place. D. A physical change has occurred. 8.According to result shown in diag. 3, what is the best inference can you get? A. Soil is insoluble. B. Soil is insoluble or partly soluble. C. Soil is soluble. D. Only water goes through a filter paper. 9. A drop of the filtrate was placed on a clear glass slide and slightly heated. There was a white residue left on the glass . What inference can you take now? A. Soil is insoluble. B. Soil is insoluble or partly soluble. C. Soil has a soluble substance. D. Filtrate is heterogeneous. 10. ![]() Find the incorrect statement regarding this current generating cell. A. Zinc oxidizes. B Carbon oxidizes. C. Zinc ionizes. D. Zinc dissolves. ANSWERS. 1- A, 2- B , 3. -A, 4. - A, 5.- C, 6.- B, 7, - D, 8. - B 9.- C, 10.- B. Highlight to get the answers. |
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