Question

A piece of red-hot magnesium ribbon will continue to burn in an atmosphere of \(\mathrm{CO}_{2}\) even though \(\mathrm{CO}_{2}\) does not support combustion. Explain.

Short answer

Magnesium can burn in \( \mathrm{CO}_2 \) by reducing it to carbon while forming magnesium oxide.

Step-by-step solution

Understanding Combustion

Combustion generally requires a fuel, oxygen, or an oxygen-containing compound to proceed. In this case, magnesium ribbon acts as the fuel but given that \( \mathrm{CO}_2 \) typically does not support combustion, we need to explore why it still proceeds.

Role of Magnesium

Magnesium, particularly when heated strongly, is a very reactive metal. It can strip oxygen from other substances due to its high affinity for oxygen. This allows it to combust in environments that would typically not support combustion, like in \( \mathrm{CO}_2 \).

Reaction with Carbon Dioxide

In the presence of \( \mathrm{CO}_2 \), red-hot magnesium will react with carbon dioxide to form magnesium oxide (\( \mathrm{MgO} \)) and carbon (\( \mathrm{C} \)). This reaction is possible because magnesium is able to reduce carbon dioxide by removing its oxygen.

Chemical Equation

The chemical reaction taking place is: \[ 2\mathrm{Mg} + \mathrm{CO}_2 \rightarrow 2\mathrm{MgO} + \mathrm{C} \] This shows that magnesium can burn in \( \mathrm{CO}_2 \) by using the oxygen from \( \mathrm{CO}_2 \), releasing carbon as a byproduct.

Conclusion

The burning of magnesium in \( \mathrm{CO}_2 \) is a redox reaction where \( \mathrm{Mg} \) is oxidized to \( \mathrm{MgO} \), and \( \mathrm{CO}_2 \) is reduced to \( \mathrm{C} \). This is possible due to magnesium's high reactivity.

Key concepts

Combustion

Combustion is a chemical process that typically involves the reaction of a fuel with oxygen, resulting in the release of heat and light, often in the form of flames. When we think of combustion, we generally imagine a scenario where there is plenty of oxygen supporting the burning process. Yet, it’s important to note that not all substances that burn require pure oxygen. Some chemical reactions may utilize other oxygen-containing compounds.

• For magnesium, a highly reactive metal, the presence of oxygen isn’t strictly necessary because it can extract oxygen from other sources.
• Typical combustion will see a fuel like gasoline reacting with oxygen in the air to form carbon dioxide and water, releasing energy.

In unique cases such as magnesium burning in a carbon dioxide environment, the process is aided by magnesium’s ability to tap into oxygen molecules available in compounds like CO₂.

Redox Reaction

A redox reaction is a type of chemical reaction that involves the transfer of electrons between two species. This is pivotal in many chemical processes, where one substance is oxidized (loses electrons) and another is reduced (gains electrons).

• Oxidation refers to the loss of electrons or an increase in oxidation state.
• Reduction implies the gain of electrons or a decrease in oxidation state.

In the context of magnesium burning in carbon dioxide, magnesium undergoes oxidation as it loses electrons to form magnesium oxide. Simultaneously, carbon dioxide is reduced to elemental carbon as it gains electrons. Thus, this process epitomizes a redox reaction.

Magnesium Reactions

Magnesium is renowned for its high reactivity, particularly when exposed to high temperatures. As a Group 2 alkaline earth metal, its reaction characteristics are profound, especially in high-energy environments. When magnesium is ignited, its reactivity enables it to interact with substances that might not typically be considered combustible.

• The reaction of magnesium with carbon dioxide illustrates its impressive chemical versatility.
• Magnesium will combust in CO₂ because it can effectively decompose the carbon dioxide, utilizing its oxygen to continue burning.

This behavior underlines magnesium's chemical strength, allowing it to burn in an environment that traditionally does not support combustion, like a CO₂-rich atmosphere.

Oxygen Affinity

Oxygen affinity describes the tendency of a substance to attract and bind with oxygen. Metals like magnesium exhibit high oxygen affinity, which is a measure of how strongly they can pull oxygen from surrounding compounds. This property is central to the reaction of magnesium with carbon dioxide.

• When magnesium is heated, its affinity for oxygen allows it to efficiently strip oxygen atoms from CO₂ molecules.
• Mg’s ability to do so makes it a potent reducing agent, meaning it can "steal" oxygen very readily from less reactive compounds.

In the combustion process, magnesium's oxygen affinity enables it to bypass the normal limitations present in non-combustible environments, illustrating its unique chemical properties.