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Reaction Types I: Combination and Decomposition

Section A: Combination Reactions

Question 1mcq
Which equation represents a combination reaction?
A.CaCO3→CaO+CO2CaCO_3 \rightarrow CaO + CO_2
B.CaO+H2O→Ca(OH)2CaO + H_2O \rightarrow Ca(OH)_2
C.Zn+CuSO4→ZnSO4+CuZn + CuSO_4 \rightarrow ZnSO_4 + Cu
D.AgNO3+NaCl→AgCl+NaNO3AgNO_3 + NaCl \rightarrow AgCl + NaNO_3
Question 2mcq
When magnesium burns in oxygen, the reaction type is mainly:
A.Photolytic decomposition
B.Double displacement reaction
C.Neutralisation only
D.Combination reaction
Question 3mcq
Combination and decomposition reactions are often considered opposite because:
A.Both involve only metals
B.Both always form precipitates
C.Combination forms one product, while decomposition breaks one reactant into simpler products
D.Both always need sunlight
Question 4mcq
Classify: 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O.
A.Precipitation reaction
B.Combination reaction
C.Displacement reaction
D.Decomposition reaction
Question 5mcq
The reaction CaO+H2O→Ca(OH)2+heatCaO + H_2O \rightarrow Ca(OH)_2 + heat is also:
A.Endothermic
B.Electrolytic only
C.Photolytic
D.Exothermic
Question 6mcq
Which feature best confirms a combination reaction?
A.One reactant produces many products
B.A metal replaces another metal
C.Two compounds exchange ions
D.Two or more reactants produce a single product

Section B: Decomposition Reactions

Question 7mcq
The reaction CaCO3→heatCaO+CO2CaCO_3 \xrightarrow{heat} CaO + CO_2 is:
A.Photolytic decomposition
B.Combination
C.Thermal decomposition
D.Double displacement
Question 8mcq
Breaking water into hydrogen and oxygen using electricity is:
A.Thermal decomposition
B.Photolytic decomposition
C.Precipitation
D.Electrolytic decomposition
Question 9mcq
Silver chloride turning grey in sunlight is an example of:
A.Combination
B.Neutralisation
C.Photolytic decomposition
D.Displacement
Question 10mcq
Classify: 2Pb(NO3)2→heat2PbO+4NO2+O22Pb(NO_3)_2 \xrightarrow{heat} 2PbO + 4NO_2 + O_2.
A.Combination
B.Double displacement
C.Thermal decomposition
D.Displacement
Question 11mcq
Most decomposition reactions require energy. Therefore they are usually:
A.Always redox-free
B.Endothermic
C.Always precipitation reactions
D.Always neutralisation reactions
Question 12mcq
Which equation shows the opposite pattern of A+B→ABA+B\rightarrow AB?
A.AB→A+BAB\rightarrow A+B
B.AB+CD→AD+CBAB+CD\rightarrow AD+CB
C.A+BC→AC+BA+BC\rightarrow AC+B
D.A→AA\rightarrow A