The preexponential and activation energy for the diffusion of chromium in nickel are \(1.1 \times 10^{-4}\) \(\mathrm{m}^{2} / \mathrm{s}\) and \(272,000 \mathrm{~J} / \mathrm{mol}\), respectively. At what temperature will the diffusion coefficient have a value of \(12 \times 10^{-14} \mathrm{~m}^{2} / \mathrm{s} 2\)

Short Answer

Expert verified
Answer: The temperature at which the diffusion coefficient has a value of 12 x 10^{-14} m²/s is approximately 1424 Kelvin.

Step by step solution

01

Identify the given information and the Arrhenius equation.

The problem provides us with the preexponential factor (D0), the activation energy (Q) and the desired diffusion coefficient (D). The Arrhenius equation for diffusion is: D = D0 * exp(-Q / (R * T)), where D is the diffusion coefficient, D0 is the preexponential factor, Q is the activation energy, R is the gas constant (8.314 J/mol K), and T is temperature in Kelvin. We are given D0 = 1.1 x 10^{-4} m²/s, Q = 272,000 J/mol, and D = 12 x 10^{-14} m²/s. We must solve for T.
02

Rearrange the equation to solve for T.

To solve for temperature, we need to isolate T in the equation. First, divide both sides by D0: D / D0 = exp(-Q / (R * T)). Now, take the natural logarithm of both sides: ln(D / D0) = -Q / (R * T). Next, multiply both sides by -(R * T): -R * T * ln(D / D0) = Q. Finally, divide both sides by (-R * ln(D / D0)): T = Q / (-R * ln(D / D0)). Now we can plug in the given values to find T.
03

Use the given values to calculate the temperature.

Substitute the given values into the equation for T: T = (272,000 J/mol) / (-(8.314 J/mol K) * ln((12 x 10^{-14} m²/s) / (1.1 x 10^{-4} m²/s))). Now we can compute the value of T: T ≈ 1424 K.
04

Report the result

The temperature at which the diffusion coefficient will have a value of 12 x 10^{-14} m²/s is approximately 1424 Kelvin.

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Key Concepts

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

Arrhenius equation
The Arrhenius equation plays a pivotal role in the study of temperature-dependent reaction rates, particularly in the field of chemical kinetics.
It is mathematically depicted as
\( D = D_0 \times \exp\left(-\frac{Q}{RT}\right) \)
where \(D\) is the diffusion coefficient, \(D_0\) is the pre-exponential factor (also known as the frequency factor), \(Q\) is the activation energy, \(R\) is the universal gas constant, and \(T\) is the absolute temperature in Kelvin.
Essentially, this equation indicates that the rate of a chemical reaction increases with temperature and provides a quantitative basis for the relationship between activation energy and the rate at which a reaction proceeds. This is because higher temperatures increase the number of effective collisions between reacting particles, leading to more frequent reaction events.
In educational texts or homework problems, the Arrhenius equation is commonly used to predict how changing the temperature affects the diffusion rates of substances or to calculate the energy barriers that must be overcome for reactions to take place.
Activation energy
Activation energy, symbolized as \(Q\) in thermodynamics, is a fundamental concept that characterizes the minimum energy which reacting species must possess in order to undergo a specific chemical reaction. It is considered the 'threshold' level of energy that enables reactant molecules to engage effectively and form products.
In the context of diffusion, the activation energy is associated with the energy required for atoms or molecules to move from one location to another within a material. A higher activation energy implies that particles need more energy to overcome the barriers between them, which typically results in lower diffusion rates unless higher temperatures are applied to the system.
Understanding the activation energy assists in comprehending why certain reactions occur spontaneously at room temperature while others proceed only at elevated temperatures or under specific conditions. For instance, a matchstick will not light until it is struck against a suitable surface, which provides the necessary activation energy for combustion.
Temperature calculation
Temperature calculation in the scope of the Arrhenius equation and diffusion problems involves rearranging the original formula to solve for the temperature variable \(T\).
This typically requires the application of logarithms to deal with the exponential nature of the equation. Once the formula is modified to isolate \(T\), it becomes possible to compute the temperature by substituting the known values of the diffusion coefficient \(D\), the pre-exponential factor \(D_0\), and the activation energy \(Q\), along with the gas constant \(R\).
Calculating temperature is quintessential for experimental design and for predicting the behavior of substances under varying thermal conditions. Accurate estimations of active temperatures can lead to better control over reaction rates in industrial processes and contribute to an understanding of material properties in various environmental conditions.

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Most popular questions from this chapter

Antimony atoms are to be diffused into a silicon wafer using both predeposition and drive-in heat treatments; the background concentration of \(\mathrm{Sb}\). in this silicon material is known to be \(2 \times 10^{20}\) atoms/m^3. The predeposition treatment is to be conducted at \(900^{\circ} \mathrm{C}\) for \(1 \mathrm{~h}\); the surface concentration of \(\mathrm{Sb}\) is to be maintained at a constant level of \(8.0 \times 10^{25}\) atoms \(/ \mathrm{m}^{3}\). Drive-in diffusion will be carried out at \(1200^{\circ} \mathrm{C}\) for a period of \(1.75 \mathrm{~h}\). For the diffusion of \(\mathrm{Sb}\) in Si, values of \(Q_{d}\) and \(D_{0}\) are \(3.65 \mathrm{eV} /\) atom and \(2.14 \times 10^{-5} \mathrm{~m}^{2} / \mathrm{s}\), respectively. (a) Calculate the value of \(Q_{0}\) - (b) Determine the value of \(x_{j}\) for the drive-in diffusion treatment. (c) Also, for the drive-in treatment, compute the position \(x\) at which the concentration of \(S b\) atoms is \(5 \times 10^{23}\) atoms/m \(^{3}\)

(a) Briefly explain the concept of a driving force. (b) What is the driving force for steady-state diffusion?

Self-diffusion involves the motion of atoms that are all of the same type; therefore, it is not subject to observation by compositional changes, as with interdiffusion. Suggest one way in which selfdiffusion may be monitored.

A sheet of BCC iron \(2-\mathrm{mm}\) thick was exposed to a carburizing gas atmosphere on one side and a decarburizing atmosphere on the other side at \(675^{\circ} \mathrm{C}\). After reaching steady state, the iron was quickly cooled to room temperature. The carbon concentrations at the two surfaces of the sheet were determined to be \(0.015\) and \(0.0068\) wt \(\%\), respectively. Compute the diffusion coefficient ifthe diffusion flux is \(7.36 \times 10^{-9} \mathrm{~kg} / \mathrm{m}^{2}+\mathrm{s}\). Hint: Use Equation \(4.9\) to convert the concentrations from weight percent to kilograms of carbon per cubic meter of iron.

When \(\alpha\)-iron is subjected to an atmosphere of ( nitrogen gas, the concentration of nitrogen in the iron, \(C_{\mathrm{N}}\) (in weight percent), is a function of hydrogen pressure, \(p_{\mathrm{N}_{2}}\) (in \(\left.\mathrm{MPa}\right)\), and absolute temperature \((T)\) according to $$ C_{\mathrm{N}}=4.90 \times 10^{-3} \sqrt{p_{\mathrm{N}_{2}}} \exp \left(-\frac{37,600 \mathrm{~J} / \mathrm{mol}}{R T}\right) $$ Furthermore, the values of \(D_{0}\) and \(Q_{d}\) for this diffusion system are \(5.0 \times 10^{-7} \mathrm{~m}^{2} / \mathrm{s}\) and \(77,000 \mathrm{~J} / \mathrm{mol}\), respectively. Consider a thin iron membrane 1.5-mm thick at \(300^{\circ} \mathrm{C}\). Compute the diffusion flux through this membrane if the nitrogen pressure on one side of the membrane is \(0.10 \mathrm{MPa}(0.99 \mathrm{~atm})\) and on the

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