In the refining of silver,the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.

Why is respiration considered an exothermic reaction? Explain.

What is a balanced chemical equation? Why should chemical equations be balanced?

Translate the following statements into chemical equations and then balance them.
$(a)$ Hydrogen gas combines with nitrogen to form ammonia.
$(b)$ Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
$(c)$ Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
$(d)$ Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Write the balanced chemical equation for the following and identify the type of reaction in each case.
$(a)$ Potassium bromide $(aq) +$ Barium iodide $(aq) \rightarrow$ Potassium iodide $(aq) +$ Barium bromide $(s)$
$(b)$ Zinc carbonate $(s) \rightarrow$ Zinc oxide $(s) +$ Carbon dioxide $(g)$
$(c)$ Hydrogen $(g) +$ Chlorine $(g) \rightarrow$ Hydrogen chloride $(g)$
$(d)$ Magnesium $(s) +$ Hydrochloric acid $(aq) \rightarrow$ Magnesium chloride $(aq) +$ Hydrogen $(g)$

Balance the following chemical equations:
$(a)$ $HNO_{3} + Ca(OH)_{2} \longrightarrow Ca(NO_{3})_{2} + H_{2}O$
$(b)$ $NaOH + H_{2}SO_{4} \longrightarrow Na_{2}SO_{4} + H_{2}O$
$(c)$ $NaCl + AgNO_{3} \longrightarrow AgCl + NaNO_{3}$
$(d)$ $BaCl_{2} + H_{2}SO_{4} \longrightarrow BaSO_{4} + HCl$