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Chapter 6: Problem 107

From a thermochemical point of view, explain why a carbon dioxide fire extinguisher or water should not be used on a magnesium fire.

Short Answer

Expert verified
A carbon dioxide fire extinguisher or water should not be used on a magnesium fire because the reactions of magnesium with both carbon dioxide and water are exothermic, producing more heat and combustible materials rather than extinguishing the fire. Therefore, using them could intensify the fire instead of extinguishing it.

Step by step solution

01

Understanding the reaction of magnesium with carbon dioxide

Magnesium is a highly reactive metal. When it reacts with carbon dioxide, which is the main component of a carbon dioxide fire extinguisher, rather than extinguishing the fire, it results in a chemical reaction that produces magnesium oxide and elemental carbon. This process is represented by the following balanced chemical equation: \(Mg_{(s)} + CO2_{(g)} → MgO_{(s)} + C_{(s)}\). This reaction is exothermic, meaning it releases heat, which can potentially feed the fire instead of extinguishing it.
02

Understanding the reaction of magnesium with water

When magnesium comes into contact with water, it reacts vigorously producing magnesium hydroxide and hydrogen gas. This is represented by the following chemical equation: \(Mg_{(s)} + 2H2O_{(l)} → Mg(OH)2_{(s)} + H2_{(g)}\). This reaction is also exothermic and the hydrogen gas produced can easily catch fire, leading to an even more intense fire.
03

Understanding Fire Extinguishing Principles

The principal mechanism for fire extinguishing usually involves removing heat from the combustion zone or decreasing the concentration of combustible material. Nevertheless, as we have learnt, the reactions of magnesium with both carbon dioxide and water are exothermic and also result in combustible materials. This is why water or a carbon dioxide fire extinguisher should not be used on a magnesium fire as it could make the situation worse by fueling the fire instead of extinguishing it.

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Most popular questions from this chapter

The combustion of \(0.4196 \mathrm{~g}\) of a hydrocarbon releases \(17.55 \mathrm{~kJ}\) of heat. The masses of the products are \(\mathrm{CO}_{2}=1.419 \mathrm{~g}\) and \(\mathrm{H}_{2} \mathrm{O}=0.290 \mathrm{~g} .\) (a) What is the empirical formula of the compound? (b) If the approximate molar mass of the compound is \(76 \mathrm{~g}\), calculate its standard enthalpy of formation.

Stoichiometry is based on the law of conservation of mass. On what law is thermochemistry based?

The work done to compress a gas is \(74 \mathrm{~J}\). As a result, \(26 \mathrm{~J}\) of heat is given off to the surroundings. Calculate the change in energy of the gas.

You are given the following data: $$ \begin{array}{c} \mathrm{H}_{2}(g) \longrightarrow 2 \mathrm{H}(g) \quad \Delta H^{\circ}=436.4 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{Br}_{2}(g) \longrightarrow 2 \mathrm{Br}(g) \quad \Delta H^{\circ}=192.5 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{H}_{2}(g)+\mathrm{Br}_{2}(g) \longrightarrow 2 \mathrm{HBr}(g) \\ \Delta H^{\circ}=-72.4 \mathrm{~kJ} / \mathrm{mol} \end{array} $$ Calculate \(\Delta H^{\circ}\) for the reaction $$ \mathrm{H}(g)+\operatorname{Br}(g) \longrightarrow \operatorname{HBr}(g) $$

A gas expands and does \(P-V\) work on the surroundings equal to \(325 \mathrm{~J}\). At the same time, it absorbs \(127 \mathrm{~J}\) of heat from the surroundings. Calculate the change in energy of the gas.
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