Chemical Reactions and Eqn

Question 1

chemical reaction

Answer 1

process in which new substances with new properties are formed when a rearrangement of atoms takes place between reacting substance and products are formed

Question 2

what can be observed when magnesium is burned in air

Answer 2

magnesium reacts with oxygen to form magnesium oxide
it burns with a dazzling white flame and releases a lot of energy
2Mg + O2 —-> 2 MgO

Question 3

examples of chemical reactions where gas is evolved

3

Answer 3

zinc granules react with hydrochloric acid to form zinc chloride and hydrogen gas
Zn + 2HCl —> ZnCl2 + H2
zinc granules react with sulfuric acid to form zinc sulfate and hydrogen gas
Zn + 2H2SO4 → ZnSO4+2H2
sodium carbonate reacts with dilute hydrochloric acid to form sodium chloride, carbon dioxide and water
Na2CO3 + 2HCl —> 2NaCl + H2O + CO2

Question 4

what is a precipitate

Answer 4

solid product formed which separates out of solution during a chemical reaction

Question 5

examples of formation of precipitate (3)

Answer 5

potassium iodide reacts with lead nitrate to form yellow precipitate of lead iodide and potassium nitrate
KI + Pb(NO3)2 —> KNO3 + PbI2
sulfuric acid reacts with barium chloride to form white precipitate of barium sulfate and hydrochloric acid
H2SO4 + BaCl2 —> BaSO4 + 2HCl
calcium hydroxide reacts with carbon dioxide to form calcium carbonate which is a white ppt along with water
Ca(OH)2 + CO2 —> CaCO3 + H2O

Question 6

example of change in color

Answer 6

when green colored copper carbonate is heated, it turns into black colored copper oxide
CuCO3 —> CuO + CO2

Question 7

example of exothermic (4)

Answer 7

CaO + H2O —> Ca(OH)2
Zn + H2SO4 –> ZnSO2 + H2
carbon burns in oxygen to form carbon dioxide
C + O2 —> CO2 + heat
natural gas (methane) burns in oxygen of air to form carbon dioxide, water and a lot of heat
CH4 + 2O2 —> CO2 + 2H2O + heat

Question 8

example of endothermic (3)

Answer 8

barium hydroxide reacts with ammonium chloride to form barium chloride, ammonia and water
Ba(OH)2 + NH4Cl —> BaCl2 + NH3 + H2O
nitrogen and oxygen are heated to a very high temp to form nitrogen monoxide
N2 + O2 + heat —-> 2NO
when calcium carbonate decomposes to form calcium oxide and carbon dioxide
CaCO3 + heat —-> CaO + CO2

Question 9

example of change in state

Answer 9

Ammonia gas reacts with hydrogen chloride gas to produce solid ammonium chloride
NH3(g) + HCl(g) —> NH4Cl(s)

Question 10

why is respiration an exothermic process?

Answer 10

because in this process glucose combines with oxygen to form CO2 and H2O along with a lot of energy
C6H12O6 + O2 —> CO2 + H20 + energy

Question 11

example of combination (4)

Answer 11

Mg + O2 —> MgO
C + O2 —-> CO2
2H2 + O2 —> 2H2O
CaO + H2O —–. Ca(OH)2

Question 12

examples of thermal decomposition (4)

Answer 12

CaCO3 —-> CaO + CO2 (thermal
2KClO3 (potassium chlorate) —–>2KCl (potassium chloride) + 3O2 (oxygen) (thermal)
FeSO4 (green) —> Fe2O3 (brown) + SO2 + SO3 (thermal)
2Pb(NO3)2 —–> 2PbO + 4NO2+O2 (thermal)

Question 13

examples of electrolysis (3)

Answer 13

H2O —> H2 + O2
2NaCl —-> 2Na + Cl2
2Al2O3 —-> 4Al + 3O2

Question 14

examples of photolysis (2)

Answer 14

AgCl (white) —-> Ag (greyish white) + Cl2

AgBr (pale yellow) —->Ag (greyish white) + Br2 (red brown)

Question 15

examples of displacement (3)

Answer 15

CuSO4 + Fe ----> FeSO4 + Cu
deep blue color of soln changes to light green
CuSO4 + Zn ---> ZnSO4 + Cu
blue soln turns colourless
CuCl2 + Pb ---> PbCl2 + Cu
green soln turns colorless

Question 16

example of double displacement

Answer 16

BaCl2 + Na2SO4 —> BaSO4 (white ppt.)+2NaCl
Pb(NO3)2 + KI —> PbI2 (yellow ppt.)+ KNO3
AgNO3 + NaCl —> AgCl (white ppt.)+ NaNO3

Question 17

example of oxidation

Answer 17

2Cu + O2 —> 2CuO

Question 18

example of redox (3)

Answer 18

CuO + H2 + heat—> Cu + H2O
ZnO + C —> Zn + CO
MnO2 + 4HCl —> MnCl + Cl2 + H2O