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Chapter 6: Problem 155

A press release announcing a new fuel-cell car to the public stated that hydrogen is "relatively cheap" and "some stations in California sell hydrogen for \(\$ 5\) a kilogram. A kg has the same energy as a gallon of gasoline, so it's like paying \(\$ 5\) a gallon. But you go two to three times as far on the hydrogen." Analyze this claim.

Short Answer

Expert verified
The claim makes two important points: hydrogen costs about the same as gasoline (per their respective energy contents), and a fuel-cell car gets two to three times as much mileage from the hydrogen as a gasoline car does from gasoline. This presumes that the hydrogen fuel-cell car is more fuel-efficient overall. However, these claims would need to be verified through scientific calculations and/or real-world tests.

Step by step solution

01

Analyze the cost comparisons

First, it is claimed that hydrogen is relatively cheap, and some stations sell it for $5 per kilogram, which is nearly the equivalent of buying a gallon of gasoline, at least in some regions. It is important not to simply assume this cost is fixed everywhere and to understand that the cost of both hydrogen and gasoline can fluctuate.
02

Compare energy capacities

Next, consider that a kilogram of hydrogen is claimed to contain the same amount of energy as a gallon of gasoline. This is something that should be verified from a scientific viewpoint because different substances usually contain differing amounts of energy per unit of mass.
03

Evaluate the efficiency claim

Lastly, the claim states that one travels two to three times farther on a kilogram of hydrogen than on a gallon of gasoline. This implies that a fuel-cell car is two to three times more fuel-efficient when using hydrogen compared to a gasoline car. To analyze this claim accurately, real-world tests or scientific calculations based on the specific energy of the fuels and the efficiency of the engines are required.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Hydrogen Fuel
Hydrogen fuel is an intriguing alternative energy source for vehicles, especially fuel-cell cars. It is comprised of hydrogen, the most abundant element in the universe, which can be used for energy production. The process of using hydrogen in fuel cells involves a chemical reaction between hydrogen and oxygen to produce electricity, water, and heat.
This makes hydrogen an attractive option due to its clean emissions, primarily water vapor, which helps in reducing pollution.
  • Abundance: Hydrogen is abundant, and it can be produced from various sources like natural gas, water, and biomass. This diversity in sourcing is key for energy security.
  • Renewability: As hydrogen can be generated from renewable energy sources like solar or wind, it supports sustainability goals. However, methods like electrolysis are energy-intensive and can impact cost-effectiveness at a larger scale.
Energy Comparison
When comparing energy, it's essential to evaluate the energy density of hydrogen versus gasoline. The statement from the exercise claims that one kilogram of hydrogen roughly equates to the energy output of one gallon of gasoline.
In scientific terms, hydrogen has a higher energy density per kilogram compared to gasoline, but gasoline packs more energy by volume due to its liquid state at normal pressure.
  • Energy Density: Hydrogen has an energy density of about 142 MJ/kg, whereas gasoline has a lower energy density per kilogram but is more energy dense per volume with about 34 MJ/L.
  • State of Matter: Hydrogen must be stored under high pressure or in a liquid state, increasing storage complexity and energy needs for compression, possibly counteracting some efficiency gains.
Fuel Efficiency
Fuel efficiency refers to how effectively a vehicle uses energy to travel a certain distance. Fuel-cell cars running on hydrogen appear to be more efficient than traditional gasoline cars. This is due to the higher intrinsic efficiency of fuel cells compared to internal combustion engines.
Fuel-cell vehicles can convert 40-60% of the hydrogen's energy into drive action, compared to the approximately 20% conversion efficiency seen in gasoline engines.
  • Efficiency Gains: This mechanical advantage allows fuel-cell vehicles to potentially travel two to three times farther on a kilogram of hydrogen than a gasoline car on the equivalent energy from gasoline.
  • Real-World Considerations: Factors like driving habits, terrain, and accessory use (air conditioning, heating) can affect real-world fuel efficiency.
Cost Analysis
Analyzing the cost of hydrogen versus gasoline involves several factors. The exercise mentions a price of \( ext{\$5}\) per kilogram of hydrogen. Pricing dynamics are complex and can vary based on region, availability, and production methods.
  • Price Variation: Unlike gasoline, which has a more established global market with fairly predictable pricing, hydrogen's cost can be influenced by local policies, the type of production technology used, and infrastructure availability.
  • Infrastructure Costs: Building hydrogen fuel stations and producing hydrogen can involve high upfront costs, though these may decrease with more widespread adoption and technological advances.
  • Operational Costs: Lower maintenance costs for fuel-cell vehicles due to fewer moving parts in the engine, but the current scarcity of service stations could increase operating expenses in less developed hydrogen markets.
Ensuring a thorough and ongoing analysis of both energy costs and operational efficiencies is key for evaluating the true economic viability of hydrogen fuel-cell vehicles.

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Most popular questions from this chapter

Predict the value of \(\Delta H_{\mathrm{f}}^{\circ}\) (greater than, less than, or equal to zero) for these elements at \(25^{\circ} \mathrm{C}:\) (a) \(\mathrm{Br}_{2}(g)\) \(\mathrm{Br}_{2}(l)\) (b) \(\mathrm{I}_{2}(g) ; \mathrm{I}_{2}(s)\)

Determine the amount of heat (in kJ) given off when \(1.26 \times 10^{4} \mathrm{~g}\) of \(\mathrm{NO}_{2}\) are produced according to the equation $$\begin{array}{r}2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g) \\\\\Delta H=-114.6 \mathrm{~kJ} / \mathrm{mol}\end{array}$$

Calculate the internal energy of a Goodyear blimp filled with helium gas at \(1.2 \times 10^{5} \mathrm{~Pa}\). The volume of the blimp is \(5.5 \times 10^{3} \mathrm{~m}^{3}\). If all the energy were used to heat 10.0 tons of copper at \(21^{\circ} \mathrm{C},\) calculate the final temperature of the metal. (Hint: See Section 5.7 for help in calculating the internal energy of a gas. 1 ton \(=9.072 \times 10^{5} \mathrm{~g} .\)

A 4.117 -g impure sample of glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) was burned in a constant-volume calorimeter having a heat capacity of \(19.65 \mathrm{~kJ} /{ }^{\circ} \mathrm{C}\). If the rise in temperature is \(3.134^{\circ} \mathrm{C},\) calculate the percent by mass of the glucose in the sample. Assume that the impurities are unaffected by the combustion process. See Appendix 2 for thermodynamic data.

The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting, that is, the conversion of \(\mathrm{ZnS}\) to \(\mathrm{ZnO}\) by heating: $$\begin{array}{r}2 \mathrm{ZnS}(s)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{ZnO}(s)+2 \mathrm{SO}_{2}(g) \\ \Delta H=-879 \mathrm{~kJ} / \mathrm{mol}\end{array}$$ Calculate the heat evolved (in kJ) per gram of ZnS roasted.
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