A reaction mechanism is defined as the sequence of reaction steps that define the pathway from reactants to products. Each step in a mechanism is an elementary reaction, which describes a single molecular event of usually one or two molecules interacting. The rate law for an overall reaction is the rate law for the slowest step in the mechanism, which is directly related to the stoichiometric coefficients of the reactants. The exception to this rule occurs when the slowest step contains intermediates. In these cases, the slowest step is usually preceded by an equilibrium step, which can be used to substitute for the intermediates in the overall rate law. Part AWhat is the rate law for the following mechanism in terms of the overall rate constant k?Step1:Step2:A+BB+C⇌→CD(fast)(slow )Express your answer in terms of k and the necessary concentrations (e. g., k*[A]^3*[D]).Part BConsider the reaction2X2Y2+Z2⇌2X2Y2Zwhich has a rate law ofrate= k[X2Y2][Z2]Select a possible mechanism for the reaction. Consider the reactionwhich has a rate law ofSelect a possible mechanism for the reaction. Step1:Step2:Step3:Z2→Z+Z (slow)X2Y2+Z→X2Y2Z (fast)X2Y2+Z→X2Y2Z (fast)Step1:Step2:X2Y2+Z2→X2Y2Z+Z (slow)X2Y2+Z→X2Y2Z (fast)Step1:Step2:X2Y2+Z2→X2Y2Z2 (slow)X2Y2Z2→X2Y2Z+Z (fast)D Step1:Step2:2X2Y2⇌X4Y4 (fast)X4Y4+Z2→2X2Y2Z (slow)E Step1:2X2Y2+Z2→2X2Y2 (slow)

One of the most useful applications of kinetics is the ability to use reaction rates to figure out the reaction mechanism. The reaction mechanism describes the sequence of elementary steps that occur to go from reactants to products. Let's start by considering the following reaction between nitrogen dioxide and carbon monoxide:

\text{NO}_2(g) + \text{CO}(g) \rightarrow \text{NO}(g) + \text{CO}_2(g) NO

2

(g)+CO(g)→NO(g)+CO

2

(g)start text, N, O, end text, start subscript, 2, end subscript, left parenthesis, g, right parenthesis, plus, start text, C, O, end text, left parenthesis, g, right parenthesis, right arrow, start text, N, O, end text, left parenthesis, g, right parenthesis, plus, start text, C, O, end text, start subscript, 2, end subscript, left parenthesis, g, right parenthesis

Based on the balanced reaction, we might hypothesize this reaction might occur from a single collision between a molecule of nitrogen dioxide and a molecule of carbon monoxide. In other words, we hypothesize this an elementary reaction. What is an elementary reaction?

In that case, we can use the stoichiometry of the balanced chemical reaction to predict the rate law is first order in \text{NO}_2NO

2

start text, N, O, end text, start subscript, 2, end subscript and first order in \text{CO}COstart text, C, O, end text. To test our hypothesis, we run some kinetics experiments to get the following rate law:

\text{rate} = k[\text{NO}_2]^2rate=k[NO

2

]

2

start text, r, a, t, e, end text, equals, k, open bracket, start text, N, O, end text, start subscript, 2, end subscript, close bracket, squared

Since the experimental rate law does not match our predicted rate law, we know immediately that our reaction must involve more than one step. Reactions that involve more than one elementary step are called complex reactions. We can use the rate law to get additional Facts

Explanation:

clouds form

solid ice forms on leaves.

water droplets form on grass.