Change in colour:
Solution: A chemical reaction that causes a colour change is the heating of copper carbonate:
\[\text{CuCO}_3 \xrightarrow{\text{heat}} \text{CuO} + \text{CO}_2.\]
- Observation: Copper carbonate (green) changes to copper oxide (black).
Change in temperature:
Solution: An example is the exothermic reaction of quicklime with water:
\[\text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{Heat}.\]
- Observation: The reaction releases heat, causing a rise in temperature.
Formation of precipitate:
Solution: An example is the reaction between sodium sulfate and barium chloride:
\[\text{Na}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4 \downarrow + 2\text{NaCl}.\]
- Observation: A white precipitate of barium sulfate (\(\text{BaSO}_4\)) is formed.
For a reaction, \[ {N}_2{O}_5(g) \rightarrow 2{NO}_2(g) + \frac{1}{2} {O}_2(g) \] in a constant volume container, no products were present initially. The final pressure of the system when 50% of the reaction gets completed is:
In Carius method for estimation of halogens, 180 mg of an organic compound produced 143.5 mg of AgCl. The percentage composition of chlorine in the compound is ___________%. [Given: Molar mass in g mol\(^{-1}\) of Ag = 108, Cl = 35.5]