What Are Reactions In Chemistry

Study Of Nuclear Reactions

A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as fission and fusion. Some early evidence for nuclear fission was the formation of a short-lived radioisotope of barium which was isolated from neutron irradiated uranium . At the time, it was thought that this was a new radium isotope, as it was then standard radiochemical practice to use a barium sulfate carrier precipitate to assist in the isolation of radium. More recently, a combination of radiochemical methods and nuclear physics has been used to try to make new ‘superheavy’ elements it is thought that islands of relative stability exist where the nuclides have half-lives of years, thus enabling weighable amounts of the new elements to be isolated. For more details of the original discovery of nuclear fission see the work of Otto Hahn.

Uses Within Geology Biology And Forensic Science

Cosmogenic isotopes are formed by the interaction of cosmic rays with the nucleus of an atom. These can be used for dating purposes and for use as natural tracers. In addition, by careful measurement of some ratios of stable isotopes it is possible to obtain new insights into the origin of bullets, ages of ice samples, ages of rocks, and the diet of a person can be identified from a hair or other tissue sample. .

Biology

Within living things, isotopic labels can be used to probe how the complex web of reactions which makes up the metabolism of an organism converts one substance to another. For instance a green plant uses light energy to convert water and carbon dioxide into glucose by . If the oxygen in the water is labeled, then the label appears in the oxygen gas formed by the plant and not in the glucose formed in the chloroplasts within the plant cells.

For biochemical and physiological experiments and medical methods, a number of specific isotopes have important applications.

Chemical Vs Physical Changes

In a physical change, a compounds shape may change, but its chemical identity will not. For example, freezing or boiling water is a physical change. Once melted or boiled, the water may be in a different form , but it is still water, H2O, and it still has the same chemical composition.

A chemical change happens when a substances chemical identity changes. An example of this is rusting. When an iron nail comes into contact with water and is then exposed to the air, it rusts, forming a brown-red substance. This process changes the chemical composition of the original substance.

While some physical changes are easily reversible, such as re-freezing melted ice, reversing a chemical change requires another chemical reaction.

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List Of Common Reactions And Examples

• Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
• B.A., Physics and Mathematics, Hastings College

A chemical reaction is a process generally characterized by a chemical change in which the starting materials are different from the products. Chemical reactions tend to involve the motion of electrons, leading to the formation and breaking of chemical bonds. There are several different types of chemical reactions and more than one way of classifying them. Here are some common reaction types:

Meaning Of Water In Chemical Reactions

In chemical reactions, water can act in many ways. Some of these include as a hydrogen bond donor or acceptor, as well as a proton donor or acceptor, which allows water to facilitate reactions in many ways.

Most importantly, water acts as a solvent in many chemical reactions. In many chemical contexts, the chemical reaction does not take place without water. Here, water allows these reactions to proceed.

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The Chemistry Of Combustion

The Fuse School – Global Education

Fire is a chemical chain reaction which takes place with the evolution of heat and light. In order for a fire to take place there are 3 main ingredients that must be present: Oxygen, Heat and Fuel.

In chemistry we call the type of reaction that produces fire a combustion reaction. Combustion is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.

Whenever we complete a combustion reaction a hydrocarbon there are generally the same products formed: CO2 and H2O.

Example

The fuel you burn in your car’s engine contains octane, C8H18. When octane is burned, the products are CO2 and H2O.

2C8H18 + 25O2 16CO2 + 18H2O

The key ingredient to the process is the availability of oxygen. Combustion cannot take place in an atmosphere devoid of oxygen.

So if you have a bottle of gasoline sitting around and open to the atmosphere which contains oxygen, why doesnt it just burst into flames?

The answer to this question is the need to overcome the activation energy of the reaction, which means that it requires energy at first to “jump start” the process. In your car, the distributor and battery provide this starting energy by creating an electrical “spark”. Other sources of initial energy can come from the Sun, matches, friction, etc.

The combustion reaction itself is quite exothermic.

FlinnScientific

Dancing Gummy Bear Reaction

The dancing gummy bear is a reaction between sugar and potassium chlorate, which produces violet fire and a lot of heat. It’s an excellent introduction to the art of pyrotechnics because sugar and potassium chlorate are representative of a fuel and oxidizer, such as you might find in fireworks. There’s nothing magical about the gummy bear. You can use any candy to supply the sugar. Depending on how you perform the reaction, though, you may get more of a sudden immolation than a bear tango.

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Review What Happens During A Physical Change And Introduce The Idea Of Chemical Change

Tell students that in previous chapters they have studied different aspects of physical change. When atoms and molecules speed up or slow down, that is a physical change. When they change state from liquid to solid or from gas to liquid, that is a physical change. When a substance is dissolved by water or some other solvent, a new substance has not really been formed. The ions or molecules can still come back together to form the original substance.

Let students know that in this chapter they will explore what happens during a chemical change. In a chemical change, the atoms in the reactants rearrange themselves and bond together differently to form one or more new products with different characteristics than the reactants. When a new substance is formed, the change is called a chemical change.

Hydrogen Bonding With Compounds

As water is a polar molecule, it is also able to dissolve any polar substance. In a similar way to the previous example of ionic compounds, the water molecules arrange themselves in such as way as to protect specific parts needed of a polar molecule. This might not cause the splitting of bonds such as in the example with ionic salts, but rather might rely on both its polar properties and also its hydrogen bonding properties.

Water can interact with substances that are able to form hydrogen bonds to dissolve them, thus making them more mobile in water and allowing reactions to take place. It can act both as a hydrogen bond acceptor and donor. Here, the compound in question will stay the same and be unchanged, yet its dissolution will provide greater means for chemical reactions to take place.

Compound + \ => Compound + \

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Evidence For Chemical Reactions

Evidence for a chemical reaction can include any of the following:

• Bubbles Many chemical reactions you see in the science lab make a chemical which is a gas, so you see bubbles.
• A colour change If the new chemicals are a different colour from the original chemicals, there will be a colour change.
• A large energy change Many chemical reactions give off lots of energy, like burning, and a few absorb energy, so they feel cold.

A new substance must be produced for a chemical reaction to take place.

The water inside a kettle has bubbles but thats just because it is boiling. Bubbles of steam form in boiling water. These bubbles do not indicate a new substance has been formed because, when cooled, the steam condenses back into liquid water. Boiling is a physical change, not a chemical reaction.

There is a colour change when you add a teabag to a mug of boiling water. Why is this not a chemical reaction?

The chemicals in the tea are dissolving in the water, and dissolving is not a chemical reaction it is a physical change.

Proust: Law Of Constant Composition

Joseph Proust was a French actor who followed in Lavoisiers footsteps. Proust performed dozens of chemical reactions, starting with different amounts of various materials. Over time he observed that no matter how he started a certain chemical reaction, the ratio in which the reactants were consumed was always constant. For example, he worked extensively with copper carbonate and no matter how he changed the ratio of starting reactants, the copper, carbon, and oxygen all reacted together in a constant ratio . As a result, in the last few years of the 18th century, Proust formulated the law of constant composition .

He realized that any given chemical substance always consisted of the same ratio by mass of its elemental parts regardless of the method of preparation. This was a huge step forward in modern chemistry since it had been previously believed that the substances formed during chemical reactions were random and disordered.

Figure 4

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Introduce The Chemical Equation For The Combustion Of Methane And Explain That Atoms Rearrange To Become Different Molecules

Explain to students that wax is made of long molecules called paraffin and that paraffin is made up of only carbon atoms and hydrogen atoms bonded together. Molecules made of only carbon and hydrogen are called hydrocarbons. Tell students that you will use the simplest hydrocarbon as a model to show how the wax, or any other hydrocarbon, burns.

Show students that there is methane and oxygen on the left side of the chemical equation and carbon dioxide and water on the right side. Explain that the molecules on the left side are the reactants and the ones on the right side are the products. When the candle was burning, the paraffin reacted with oxygen in the air to produce carbon dioxide and water, similar to the chemical reaction between methane and oxygen.

Explain to students that the chemical formula for methane is CH4. This means that methane is made up of one carbon atom and four hydrogen atoms.

Show students that the other reactant is two molecules of oxygen gas. Point out that each molecule of oxygen gas is made up of two oxygen atoms bonded together. It can be confusing for students that oxygen the atom, and oxygen the molecule, are both called oxygen. Let students know that when we talk about the oxygen in the air, it is always the molecule of oxygen, which is two oxygen atoms bonded together, or O2.

Introduce Two Other Combustion Reactions And Have Students Check To See Whether Or Not They Are Balanced

Tell students that, in addition to the wax and methane, some other common hydrocarbons are propane , and butane . Have students count the number of carbon, hydrogen, and oxygen atoms in the reactants and products of each equation to see if the equation is balanced. They should record the number of each type of atom in the chart on their activity sheet.

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Common Types Of Biological Reactions

Within biological systems there are six major classes of biochemical reactions that are mediated by enzymes. These include group transfer reactions, the formation/removal of carbon-carbon double bonds, isomerization reactions, ligation reactions, hydrolysis reactions, and oxidation-reduction reactions. This section will give you a brief introduction to these six types of reactions and then the following section will focus more in-depth on oxidation-reductions and how they are critical for the formation of the major form of cellular energy, adenosine triphosphate . Note that all of these reaction types require an enzyme catalyst to speed up the rate of the reactions within biological systems.

Group Transfer Reactions

In group transfer reactions, a functional group will be transferred from one molecule that serves as the donor molecule to another molecule that will be the acceptor molecule. The transfer of an amine functional group from one molecule to another is common example of this type of reaction and is shown in Figure 7.3 below.

The Formation/Removal of Carbon-Carbon Double Bonds

Figure 7.4 Hydrogenation of Oils to Produce Margarine. Unsaturated oils can by partially or fully hydrogenated to produce the saturated fatty acids to produce margarines that will remain solid at room temperature. The addition of the new hydrogen atoms to create the saturated hydrocarbons are shown in yellow in the final product.

Isomerization Reactions

Ligation Reactions

Hydrolysis Reactions

How Are Chemical Reactions Classified

Chemists classify chemical reactions in a number of ways: by type of product, by types of reactants, by reaction outcome, and by reaction mechanism. Often a given reaction can be placed in two or even three categories, including gas-forming and precipitation reactions. Many reactions produce a gas such as carbon dioxide, hydrogen sulfide, ammonia, or sulfur dioxide. Cake batter rising is caused by a gas-forming reaction between an acid and baking soda . Classification by types of reactants include acid-base reactions and oxidation-reduction reactions, which involve the transfer of one or more electrons from a reducing agent to an oxidizing agent. Examples of classification by reaction outcome include decomposition, polymerization, substitution, and elimination and addition reactions. Chain reactions and are examples of classification by reaction mechanism, which provides details on how atoms are shuffled and reassembled in the formation of products.

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Determine Relative Reaction Rates And Further Mechanistic Understanding

Calow, A. D. J., Carbó, J. J., Cid, J., Fernández, E., & Whiting, A. . Understanding ,-Unsaturated Imine Formation from Amine Additions to ,-Unsaturated Aldehydes and Ketones: An Analytical and Theoretical Investigation. The Journal of Organic Chemistry, 79, 51635172. In previous work, the researchers had reported a catalytic method to synthesize chiral -amino alcohols via in situ generation of ,-unsaturated imines. They stated that there was a lack of kinetic or mechanistic studies regarding the relative 1,2- versus 1,4- addition of primary amines to ,-unsaturated aldehydes and ketones. To further this understanding, the researchers used in situ ReactIR spectroscopy along with NMR studies and DFT calculations, to better characterize the addition of primary amines to ,-unsaturated aldehydes and ketones and examine the relative rates of these reactions.

ReactIR data showed that when benzylamine was added to crotonaldehyde, 1,2- addition resulted exclusively whereas when benzylamine was added to methyl vinyl ketone, 1,4- addition resulted exclusively.

Read A Brief Summary Of This Topic

chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituentatoms of the reactants to create different substances as products.

Chemical reactions are an integral part of technology, of culture, and indeed of life itself. Burning fuels, smeltingiron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.

Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. No matter what its physical state, water is the same compound, with each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquid, or vapour, encounters sodium metal , the atoms will be redistributed to give the new substances molecular hydrogen and sodium hydroxide . By this, we know that a chemical change or reaction has occurred.

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Guide Students As You Answer The Following Question Together:

How many carbon, hydrogen, and oxygen atoms are in the reactants compared to the number of carbon, hydrogen, and oxygen atoms in the products?

Show students how to use the big number in front of the molecule and the little number after an atom of the molecule to count the atoms on both sides of the equation. Explain to students that the subscript tells how many of a certain type of atom are in a molecule. The coefficient tells how many of a particular type of molecule there are. So if there is a coefficient in front of the molecule and a subscript after an atom, you need to multiply the coefficient times the subscript to get the number of atoms.

For example, in the products of the chemical reaction there are 2H2O. The coefficient means that there are two molecules of water. The subscript means that each water molecule has two hydrogen atoms. Since each water molecule has two hydrogen atoms and there are two water molecules, there must be 4 hydrogen atoms.