Problem 87 - Chemistry The Science in Context

Question

Methane can serve as the fuel for electric cars powered by fuel cells. Carbon dioxide is a product of the fuel cell reaction. All cars powered by internal combustion engines burning natural gas (mostly methane) produce \(\mathrm{CO}_{2}\). Why are electric vehicles powered by fuel cells likely to produce less \(\mathrm{CO}_{2}\) per mile?

Step-by-Step Solution

Answer

Answer: Electric vehicles powered by fuel cells produce less CO2 per mile compared to internal combustion engines burning natural gas mainly because fuel cells have higher efficiency and do not directly produce CO2 during their main reaction.

Step 1: Examine fuel cell reaction

Fuel cells that use methane as the source of their fuel produce energy through a chemical reaction. The main reaction is 2H2 + O2 -> 2H2O. This reaction produces water as a byproduct, and there is usually no direct production of CO2 during this step.

Step 2: Examine internal combustion engines reaction

Internal combustion engines that burn natural gas (mostly methane) as fuel produce energy through a combustion reaction. The main reaction is CH4 + 2O2 -> CO2 + 2H2O. This reaction produces carbon dioxide (CO2) as a direct byproduct.

Step 3: Analyze the efficiency of fuel cells

Fuel cells are known to be highly efficient at converting chemical energy stored in the fuel to electrical energy. Typically, fuel cells have an efficiency of 40%-60%.

Step 4: Analyze the efficiency of internal combustion engines

In comparison, internal combustion engines are less efficient at converting the chemical energy stored in the fuel to mechanical energy. Typically, internal combustion engines have an efficiency of 25%-35%.

Step 5: Compare the CO2 emissions

Since fuel cells have a higher efficiency, they require less fuel (methane) to produce the same amount of energy as an internal combustion engine. This means that even if some CO2 is generated during the production and supply of methane for fuel cells, the overall CO2 emissions per mile would still be lower for fuel cell vehicles due to their higher efficiency. Additionally, fuel cells do not directly produce CO2 during their main reaction, making their CO2 emissions significantly lower than internal combustion engines. In conclusion, electric vehicles powered by fuel cells are likely to produce less CO2 per mile primarily because fuel cells are more efficient than internal combustion engines and do not directly produce CO2 during their main reaction.

Key Concepts

methane fuel reaction

Fuel cells using methane can provide clean energy for electric vehicles. The fundamental principle is a chemical reaction in which methane acts as the fuel source. A typical reaction involves the transformation of hydrogen and oxygen into water, represented as: \[2H_2 + O_2 \rightarrow 2H_2O\]
This reaction is clean with water as the primary byproduct, meaning no direct production of CO2 occurs in the process.
This type of reaction ensures the energy generated is used effectively in powering a vehicle, emphasizing the cleaner nature of methane-fueled cells. It's crucial to understand that while fuel cells don't directly create CO2, the process of obtaining hydrogen or methane might involve procedures releasing CO2, but this isn't a part of the cell's reaction.

• Methane acts as a hydrogen carrier for the reaction.
• Water is the byproduct of the main reaction.
• CO2 is not directly produced in fuel cells using methane.

CO2 emissions

Carbon dioxide (CO2) emissions are a significant concern in the context of global warming. In fuel cell reactions, CO2 isn't a primary issue during operation, as the reaction mainly produces water. However, CO2 can be emitted at different stages of the fuel's lifecycle, albeit less directly than in traditional vehicles.
In the fossil-fuel based internal combustion engines, burning natural gas (mostly methane) results directly in CO2 emissions, shown by the equation: \[CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O\]
CO2 is directly a byproduct of this reaction, thus contributing to overall emissions.
Fuel cells, due to their higher efficiency, require less fuel to produce the same energy as combustion engines, leading to potentially lower overall CO2 emissions. Even with the entire lifecycle considered, including production, supply, and usage of methane, fuel cell technologies tend to have a smaller carbon footprint, especially if renewable sources are leveraged for methane production.

• Internal combustion naturally produces CO2.
• Fuel cells indirectly reduce CO2 emissions.
• Lifecycle CO2 emissions vary depending on fuel production methods.

internal combustion engines efficiency

Efficiency refers to how well a machine converts energy from fuel into usable power. Internal combustion engines, commonly found in traditional vehicles, convert chemical energy in fuels like natural gas into mechanical energy. However, their efficiency ranges only from 25% to 35%, meaning a considerable portion of the energy is wasted, mostly as heat.
Compared to fuel cells, which convert chemical energy directly to electrical energy with 40%-60% efficiency, internal combustion engines are less effective. This efficiency gap means that internal combustion engines consume more fuel for the same output, leading to higher emissions per unit of energy.
Additionally, the waste heat in combustion engines requires cooling systems, which further impacts overall vehicle efficiency. Thus, while directly burning methane releases energy, the process in internal combustion is less sustainable in the long term.

• Internal combustion engines have lower efficiency.
• A greater energy loss occurs in the form of heat.
• Higher fuel use increases emissions.