Electrochemical Nature of Heterogeneous Reactions Quiz

<p>The slowest step</p> Signup and view all the answers

<p>Homogeneous reactions</p> Signup and view all the answers

<p>The rate increases</p> Signup and view all the answers

<p>$\frac{k_2}{k_1} = \frac{E_A}{R} \left(\frac{1}{T_1} - \frac{1}{T_2}\right)$</p> Signup and view all the answers

<p>Solid-gas</p> Signup and view all the answers

<p>Lattice defects and vacancies</p> Signup and view all the answers

<p>Area of the interface</p> Signup and view all the answers

<p>$r = rac{dM}{dt} = kAC$</p> Signup and view all the answers

<p>Formation of new bonds</p> Signup and view all the answers

<p>Autocatalytic reaction</p> Signup and view all the answers

<p>Non-porous nature of the product</p> Signup and view all the answers

<p>The rate increases with time</p> Signup and view all the answers

<p>The adhesion of the fluid to the surface and the viscosity of the fluid</p> Signup and view all the answers

<p>$\delta = 2r_0S_h$</p> Signup and view all the answers

<p>The rate increases</p> Signup and view all the answers

<p>Temperature only slightly affects diffusion-controlled reactions</p> Signup and view all the answers

<p>$r_A = -D \nabla C_A$</p> Signup and view all the answers

<p>Mass transfer coefficient</p> Signup and view all the answers

<p>Case 1: ks &lt;&lt; km</p> Signup and view all the answers

<p>$r_A = -k_sC_s$</p> Signup and view all the answers

<p>The rate of a chemical reaction is directly proportional to the concentrations of reactants.</p> Signup and view all the answers

<p>The Arrhenius equation is given by $\frac{d \ln k},{dT} = \frac{E_A},{RT^2}$ and it describes the relationship between the rate constant of a chemical reaction and the temperature.</p> Signup and view all the answers

<p>The van't Hoff's equation is similar to the Arrhenius equation and is given by $\frac{d \ln k},{dT} = \frac{\Delta H},{RT^2}$, where $\Delta H$ is the enthalpy change of the reaction.</p> Signup and view all the answers

<p>The activation energy is the energy barrier that must be overcome for a chemical reaction to occur. It can be determined using the Arrhenius equation by plotting the natural logarithm of the rate constant against the reciprocal of the temperature.</p> Signup and view all the answers

<p>Heterogeneous reactions involve reactants and products in different phases, while homogeneous reactions occur in a single phase.</p> Signup and view all the answers

<p>Nucleation plays an important role in heterogeneous processes such as thermal decomposition in solids, crystallization, precipitation of solids from liquids, gas evolution in liquids, deposition of solids from gases and roasting.</p> Signup and view all the answers

<p>The three steps involved in nucleation are: 1) nucleation stage or induction period, 2) formation and growth of the reaction interface during the period of acceleration, and 3) propagation of the reaction interface.</p> Signup and view all the answers

<p>If a porous product layer is formed, the rate of reaction is not affected by the coating and resistance may be due only to diffusion through the boundary layer. However, if a non-porous product layer is formed, the rate of reaction may be controlled by diffusion through this layer.</p> Signup and view all the answers

<p>An autocatalytic reaction is a type of reaction in which the liquid product reacts further with the solid reactant, leading to an increasing rate of reaction.</p> Signup and view all the answers

<p>The mass of the solid, the concentration of the reagent, and the solid/liquid ratio (pulp density) can all affect the rate of a solid-liquid reaction.</p> Signup and view all the answers

<p>The five categories of heterogeneous processes based on the nature of the interface are: (i) Solid-gas, (ii) Solid-liquid, (iii) Solid-solid, (iv) Liquid-gas, and (v) Liquid-liquid.</p> Signup and view all the answers

<p>The various lattice defects that can occur in a crystal include: (i) Schottky type of lattice defect, (ii) Frenkel type of lattice defect, (iii) Non-metal deficiency, (iv) Excess metal ions in interstitial cations, and (v) Non-metal excess.</p> Signup and view all the answers

<p>The rate of a heterogeneous reaction depends on the area of the interface. Reactions involving fine particles have a higher rate compared to those involving coarse particles.</p> Signup and view all the answers

<p>The geometry of the interface is an important factor in determining the rate of a reaction. For plates or discs, the surface area remains constant throughout the reaction, resulting in a constant rate. However, for spheres or pellets, the surface area changes as the reaction proceeds, leading to a changing rate.</p> Signup and view all the answers

<p>For a solid-liquid reaction assuming constant concentration, the rate expression is given by $r = \frac{dM},{dt} = kAC$, where $M$ is the mass of solid at time $t$, $A$ is the surface area of the solid, $C$ is the concentration of the fluid reactant, and $k$ is the rate constant.</p> Signup and view all the answers

<p>$J = -D\frac{dc}{dx}</p> Signup and view all the answers

<p>$Sh = \frac{k_ml}{D}</p> Signup and view all the answers

<p>The steps involved are: 1. diffusion of reacting molecules from the bulk of fluid to the interface, 2. adsorption at the interface, 3. reaction at the interface, 4. desorption of reaction products from the interface, and 5. diffusion of reaction products from the interface into the bulk of fluid.</p> Signup and view all the answers

<p>The mechanism of the reaction may change from diffusion to chemical reaction control with increasing reagent concentration.</p> Signup and view all the answers

<p>$E_a = R\cdot T_A - R\cdot T_B$</p> Signup and view all the answers

<p>The steps involved in solid-fluid reactions are:1. External mass transfer between the bulk fluid and the external surface of the solid.2. Diffusion of reactants and products within the pores of the solid.3. Adsorption of reactants and products on the reaction surface.4. Migration of reactants and products on the reaction surface.5. Chemical reaction between the reactants from the fluid phase and components in the solid.</p> Signup and view all the answers

<p>Fick's First Law states that the rate of diffusion of substance A per unit cross section of a solid is proportional to the concentration gradient in the direction of diffusion. The equation for the diffusion flux is $J_A = -D \nabla C_A$. Where $J_A$ is the diffusion flux, $D$ is the diffusivity (diffusion coefficient), and $\nabla C_A$ is the concentration gradient.</p> Signup and view all the answers

<p>Fick's Second Law applies when the concentration gradient changes with time as a result of diffusion itself. The equation for the diffusion flux in the case of unsteady-state diffusion is $J_A = D \nabla^2 C_A$. Where $J_A$ is the diffusion flux, $D$ is the diffusivity (diffusion coefficient), and $\nabla^2 C_A$ is the concentration gradient.</p> Signup and view all the answers

<p>The overall rate of a heterogeneous reaction is determined by the slowest step, also known as the rate-controlling step. The reaction conditions can affect which step becomes rate-controlling. It is important to understand how each step relates to the other in order to determine the overall rate of the process.</p> Signup and view all the answers

<p>If the rate of mass transfer, $n_A$, is defined per unit surface area, then the chemical reaction rate, $r_A$, at the same surface must be defined per unit area of that surface for any comparison of both rates to be done. The equations are:Rate of mass transfer: $\frac{dn_A},{dt} = \frac{km(C_b - C_s)},{\Delta x}$Rate of reaction: $\frac{dN_A},{dt} = \frac{k_r S},{\Delta x}$.Where $km$ is the mass transfer coefficient, $C_b$ and $C_s$ are the concentrations of A in the bulk and at the surface respectively, $\Delta x$ is the thickness of the stagnant film, $S$ is the area of the reaction interface, and $k_r$ is the rate constant of the chemical reaction.</p> Signup and view all the answers

<p>Sh = 2.0 + 0.6Re^{1/2}</p> Signup and view all the answers

<p>Sh = 2.0 + 0.6Re^{1/2}Sc^{1/3}</p> Signup and view all the answers

<p>Cs = -\frac{ks}{km + ks}Cb</p> Signup and view all the answers

<p>rA = -D\nabla CA</p> Signup and view all the answers

<p>rA = -ksCb</p> Signup and view all the answers