That Affect Reaction Rates

It is easy to see why reactions speed up when the concentrations of reacting molecules are increased higher concentrations (more molecules per unit volume) lead to more collisions and so to more reaction events. But reactions also speed up when the temperature is increased. Why The answer lies in the fact that not all collisions possess enough energy to break bonds. A minimum energy called the activation energy ( ) is needed for a 

The reason that a reaction occurs faster as the temperature is increased is that the speeds of the molecules increase with temperature. So at higher temperatures, the average collision is more energetic. This makes it more likely that a given collision will possess enough energy to break bonds and to produce the molecular rearrangements needed for a reaction to occur. 

Many conditions need to be met to produce a chemical reaction between molecules. 

What if all collisions between molecules resulted in a chemical reaction How would life be different  

Why does increasing the temperature speed up a chemicai reaction  

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In Lab 17.1, you learned about the effect of temperature and concentration on reaction rate. Another factor that affects reaction rate is the amount of surface area of the reactants. If a chemical reaction is to take place, the molecules of reactants must collide. Changing the amount of surface area modifies the rate of collision, and, thus, the rate of reaction. If surface area increases, collision frequency increases. If surface area decreases, so does the number of collisions. In this lab, you will examine the effect of surface area on rate of reaction. You will also determine how a combination of factors can affect reaction rate. 

Predicting Can relative reaction rates be predicted with certainty when more than one factor that affects reaction rate is involved Explain. 

V. ENVIRONMENTAL FACTORS THAT AFFECT REACTION RATE... 

Chemists have made the following observations about factors that affect reaction rate. You may already be familiar with some of these observations, from your previous studies of chemical reactions and from Investigation 6-A. 

Summary of Some Factors That Affect Reaction Rate... 

In this section, you learned how to express reaction rates and how to analyze reaction rate graphs. You also learned how to determine the average rate and instantaneous rate of a reaction, given appropriate data. Then you examined different techniques for monitoring the rate of a reaction. Finally, you carried out an investigation to review some of the factors that affect reaction rate. In the next section, you will learn how to use a rate law equation to show the quantitative relationships between reaction rate and concentration. 

The rate of a chemical reaction depends on several factors, as you learned in section 6.1. One of the factors that affect reaction rate is the concentrations of the reactants. You know that the rates of most chemical reactions increase when the concentrations of the reactants increase. Is there a more specific relationship In this section, you will explore the quantitative relationships between the rate of a reaction and the concentrations of the reactants. 

Increasing the temperature generally speeds up a reaction. Lowering the temperature of food by refrigeration causes a decrease in the rate of the bacterial action responsible for food spoilage. The factors that affect reaction rates are not desirable or undesirable in themselves and can be useful manipulators to serve a desired purpose. 

We can draw a very useful general conclusion from this simple binary system that is applicable to more complex processes changes in production rate can be achieved only by changing conditions in the reactor. This means something that affects reaction rate in the reactor must vary holdup in liquid-phase reactors, pressure in gas-phase reactors, temperature, concentrations of reactants (and products in reversible reactions), and catalyst activity or initiator addition rate. Some of these variables affect the conditions in the reactor more than others. Variables with a large effect are called dominant. By controlling the dominant variables in a process, we achieve what is called partial control. The term partial control arises because we typically have fewer available manipulators than variables we would like to control. The setpoints of the partial control loops are then manipulated to hold the important economic objectives in the desired ranges. 

Other metal ion factors that affect reaction rates of octahedral complexes include the following (relative rates for ligand exchange are indicated by the inequalities) ... 

Another type of substance that affects reaction rates is called an inhibitor. Unlike a catalyst, which speeds up reaction rates, an inhibitor is a substance that slows down, or inhibits, reaction rates. Some inhibitors, in fact, actually prevent a reaction from happening at all. 

In practice, the choice of substrate concentrations is limited by such considerations as the solubility of the substrates, the viscosity and high initial absorbance of concentrated solutions, and the relative costs of the reagents. Furthermore, the selection of appropriate substrate concentrations is only one of the factors to be considered in formulating an optimal assay system for the measurement of a specific enzyme activity. Critical choices must also be made with respect to other, frequently interdependent factors that affect reaction rate, such as the concentrations of activators and the nature and pH of the buffer system. The traditional empirical approach to optimization has been replaced by newer techniques of simplex co-optimization and response-... 

Methods in which some property related to substrate concentration (such as absorbance, fluorescence, chemiluminescence, etc.) is measured at two fixed times during the course of the reaction are known as two-point kinetic methods. They are theoreticahy the most accurate for the enzymatic determination of substrates. However, these methods are technically more demanding than equifibrium methods and all the factors that affect reaction rate, such as pH, temperature, and amount of enzyme, must be kept constant from one assay to the next, as must the timing of the two measurements. These conditions can readily be achieved in automatic analyzers. A reference solution of the analyte (substrate) must be used for calibration. To ensure first-order reaction conditions, the substrate concentration must be low compared to the K, (i.e., in the order of less than 0.2 X K, . Enzymes with high K , values are therefore preferred for kinetic analysis to give a wider usable range of substrate concentration. 

Factors That Affect Reaction Rates 16-6 Rates Transition State Theory... 

We are all familiar with processes in which some quantity changes with time— a car travels at 40 miles/hour, a faucet delivers water at 3 gallons/minute, or a factory produces 32,000 tires/day. Each of these ratios is called a rate. The rate of a reaction describes how fast reactants are used up and products are formed. Chemical kinetics is the study of rates of chemical reactions, the factors that affect reaction rates, and the mechanisms (the series of steps) by which reactions occur. 

The collision theory allows us to explain the factors that affect reaction rate. There is a wide range of energies among molecules in any sample, and generally only the most energetic molecules can undergo reaction. An increase in temperature increases the number of molecules that have sufficient energy to react. An increase in concentration or pressure... 

Rate coefficient includes all factors that affect reaction rate, except for concentration, which is explicitly accounted for. Rate coefficient is therefore not constant because of that reason the name reaction rate coefficient is preferred over reaction rate constant. The rate coefficient is mainly affected by temperature as described by Arrhenius equation but also, ionic strength, surface area of the adsorbent (for heterogeneous reactions), light irradiation, and other physicochemical properties, depending on the considered reaction. 

We explore four variables that affect reaction rates concentration, physical states of reactants, temperature, and presence of catalysts. These factors can be understood in terms of the collisions among reactant molecules that lead to reaction. 

In Reaction 2.14, heat, pressure, and catalysts are needed to convert ethylene gas to polyethylene. Explain the effects of each of the three conditions (heat, pressure, catalysts) in terms of factors that affect reaction rates. 

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