A chemical reaction's rate is defined as the rate of change in concentration of a reactant or product divided by the balanced equation's coefficient. This means that the faster a reaction proceeds, the higher its rate.
The speed at which reactions occur is important in many areas of science and technology. For example, when trying to create medicines it is desirable for their reactions with chemicals inside cells to be fast so that much-needed drugs can be produced before any effects from them are lost. When trying to break down toxic substances it is important for the reaction between water and sodium hypochlorite (bleach) to be very fast so that much bleach can be used up before it has time to damage other parts of the environment.
In chemistry class, we often study reactions by measuring how much material is left over after some fixed time. The rate of a reaction can also be measured by using a spectrophotometer to record how much of a substance absorbs light at different wavelengths. From this information, you can calculate the amount of material that does not absorb light at each wavelength, which is called the spectrum of the reaction mixture. A peak in the spectrum indicates that a reaction is taking place, even if only slowly.
The rate of reaction is described as the pace at which molecules react and generate products, or the rate at which a chemical reaction occurs. It is determined by the law of mass actions. The rate of a chemical reaction increases as the concentration of reacting species increases. The rate of a chemical reaction can also be increased by increasing the temperature or by using catalysts. In general, larger molecules tend to move through their respective mixtures more slowly than smaller ones. This is because it takes more energy for a molecule with more mass to overcome its kinetic barrier to reaction.
For example, consider the reaction 2Na+ + 2H2O → 4H+ + Na+ + O2. The rate of this reaction is greatly dependent on the mass of each ion. Ions are large molecules and thus they will react with water more slowly than small molecules such as hydrogen peroxide or oxygen gas. At any given moment, there are many more ions than molecules in solution; thus, the reaction will take place slowly until all of the ions react with water molecules. When most or all of the ions have reacted with water, then the reaction will speed up because there are now fewer particles to collide with.
Ions of similar size but with different masses would also react with water at different rates due to the law of mass action.
The pace of response 1. The pace of a reaction as represented by the change in concentration of a reactant or product over time. 2. The rate at which a reaction occurs; that is, the slope of the curve.
3. The speed at which something happens; that is, the distance traveled by a particle in a given amount of time.
4. The point at which the rate of a reaction is maximum.
The concentrations of both reactants and products fluctuate as a reaction develops, and hence the rate of the reaction varies. These interactions are described by formulas known as "rate laws" or "rate equations." The simplest rate law is that for a first-order reaction: where A = initial concentration of product (or substrate) R = reaction rate n = exponent, the number of moles of product formed per mole of substrate at time t
Rate laws get more complicated than this simple version because it assumes that the rate only changes due to fluctuations in the concentration of the reactants. In reality, the rate will also depend on other factors such as temperature, pressure, and the type of catalyst present. However, even with these complications, many reactions fit well into equation form. For example, the reaction between sodium hydrogen carbonate and water can be expressed as A(t) + B(t) = C(t), where A and B are the concentrations of reactants and C is the concentration of product at any given moment during the reaction.
If the concentration of one of the reactants remains constant, then the rate of reaction will remain constant over time.
A reaction rate is the pace at which a chemical reaction occurs. When a reaction has a low rate, it signifies that the molecules mix at a slower pace than when a reaction has a high rate. The rate of a reaction can be accelerated by heating or stirring the mixture first or adding a catalyst to speed up the reaction.
The term "reaction rate" may also be called "rate constant". The unit for measuring the rate of a reaction is called a "rate constant". For example, the rate of hydrogenation of ethyl acetate is very slow at room temperature but it can be increased by increasing the temperature. The value of the rate constant for this reaction at 25° C. is 2.1 × 10-3 mol-1 s-1.
In chemistry reactions are often described as either "slow" or "fast"; however, it should be noted that there is no exact speed limit for reactions to occur. Some reactions will always happen even if they are quite slow, while others will never happen unless they are extremely fast. A reaction's speed depends on the type of reaction involved and the conditions such as temperature and pressure under which it happens.
It is important to note that the word "reaction" itself does not have any special meaning other than what is defined below.
Reactions in Chemistry
|reaction rate||speed with which reactants turn into products|
|single replacement reactions||A chemical reaction that occurs when the atoms of one element replace the atoms of another element in a compound|
|synthesis||A chemical reaction in which two or more substances react to yeild a single product|