Rate Equation
Rate Equation - Related Videos
03:10
Chemical Equations
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2020
Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are called reactants, and their formulas are placed on the left side of the equation. The substances generated by the reaction are called products, and their formulas are placed on the right side of the equation. Plus signs (+) separate individual reactant and product formulas, and an arrow (→) separates the reactant and product (left and right)...
02:55
Thermochemical Equations
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2020
For a chemical reaction (the system) carried out at constant pressure – with the only work done caused by expansion or contraction – the enthalpy of reaction (also called the heat of reaction, ΔHrxn) is equal to the heat exchanged with the surroundings (qp). The change in enthalpy is an extensive property, and it depends on the amounts of the reactants participating in the reaction (or the number of moles of reactants). The change in enthalpy is specific to the reaction, and the physical...
02:59
The Nernst Equation
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2020
Nonstandard Reaction Conditions The interconnection between standard cell potentials and various thermodynamic parameters such as the standard free energy change ΔG° and equilibrium constant K has been previously explored. For example, a redox reaction involving zinc(II) and tin(II) ions at 1 M concentration with Eºcell = +0.291 V and ΔG° = −56.2 kJ is spontaneous. Discharge of this cell, however, results in a change in the reactant concentration and a steady decrease of the cell potential. At...
10:49
Determining Rate Laws and the Order of Reaction
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2023
Source: Laboratory of Dr. Neal Abrams — SUNY College of Environmental Science and Forestry All chemical reactions have a specific rate defining the progress of reactants going to products. This rate can be influenced by temperature, concentration, and the physical properties of the reactants. The rate also includes the intermediates and transition states that are formed but are neither the reactant nor the product. The rate law defines the role of each reactant in a reaction and can be used to...
03:08
Rate-Determining Steps
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2020
Relating Reaction Mechanisms In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate. The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
FAQs
Reaction orders are determined from kinetic behavior rather than copied directly from the balanced chemical equation. A reactant may therefore have an experimentally established power that differs from its stoichiometric coefficient. This distinction matters because the rate equation reflects how concentration changes influence reaction speed, while stoichiometry describes the overall quantitative composition of the reaction.
The rate constant summarizes the reaction’s kinetic behavior under specified conditions after the concentration terms and their experimentally determined powers are accounted for. Comparing rate constants can help chemists evaluate reaction behavior, but the comparison is meaningful only when relevant conditions are controlled. Its value therefore supports quantitative analysis rather than serving as a universal measure independent of conditions.
A rate equation allows chemists to substitute altered reactant concentrations into the concentration terms and evaluate the resulting rate relative to the original conditions. Because each concentration is raised to its reaction order, the size of the rate change depends on that experimentally determined power. This makes the equation useful for anticipating how concentration adjustments may speed up or slow down a reaction.
The concentration powers in a rate equation provide kinetic evidence about how reactants participate in the process, even though the equation alone does not simply reproduce the overall stoichiometry. Chemists compare the observed relationship with proposed reaction mechanisms to assess consistency. Agreement or disagreement can help distinguish plausible explanations for the measured reaction behavior.
Chemists determine reaction orders by analyzing kinetic data and identifying how the measured reaction rate depends on reactant concentrations. The powers are therefore empirical results, not assumptions based only on the balanced reaction equation. Once established, they can be combined with the measured rate behavior to calculate a rate constant under the conditions used for the analysis.
A rate constant should be interpreted together with the conditions under which it was determined. The overview specifically frames rate constants as values obtained under specified conditions, so transferring one value to a different chemical situation requires care. Keeping relevant conditions consistent allows chemists to compare kinetic data and use the rate equation for reliable quantitative predictions.
Chemists use rate equations to compare how different chemical systems respond to changes in reactant concentration and to evaluate their rate constants under specified conditions. These comparisons convert kinetic observations into quantitative relationships rather than relying only on qualitative labels such as fast or slow. The resulting information supports interpretation of reaction behavior and assessment of proposed mechanisms.
Rate equations support reaction optimization and process design by showing how concentration changes affect reaction speed and by providing rate constants for specified conditions. They also enable quantitative analysis of chemical systems and help organize kinetic data. In this way, the equations connect laboratory measurements with decisions about how a reaction should be evaluated or adjusted.