Module Four (Reactions)

What does an oxidation-reduction reaction involve?

It involves the transfer of electrons where one species gains electrons and one loses electrons.

Advantages of nuclear fusion

The small isotopes of hydrogen are plentiful on Earth and easy to obtain. The end products of fusion are usually light, stable nuclei rather than the heavy radioactive ones produced by fission.

What are three important things to remember about oxidation and oxidizing agents?

1. An oxidizing agent causes another substance to be oxidized. 2. The only way to cause oxidation is to remove electrons from that other substance (because oxidation is loss of electrons). 3. Therefore, the oxidizing agent is reduced as it gains electrons from the other substance.

The model for a synthesis reaction:

A + B → AB.

The model for a single replacement reaction:

A + BC → AC + B

A chemical reaction starts with a ______ and ends with a ______.

A chemical reaction starts with a reactant and ends with a product.

Describe what happens during a neutralization reaction.

A double displacement reaction in which the positive ions from one reactant take the place of the positive ions in the other reactant. Neutralizing a strong acidic solution requires chemical reactions with bases.

What are beta particles, and how are they involved in radioactive decay?

A negative beta particle is an electron that is emitted when a neutron inside the atom's nucleus breaks down into a proton and an electron. The proton stays in the nucleus, and the electron is emitted as a beta particle. This means when an atom releases a beta particle, its atomic number increases by one and its mass number stays the same.

What do coefficients in a chemical reaction indicate?

A numerical or constant quantity placed before each compound in a chemical equation to balance it.

What is an oxidizing agent?

A reactant that causes another substance to be oxidized (not being oxidized itself). The oxidizing agent is the reactant that is reduced.

What is a reducing agent?

A reactant that causes another substance to be reduced (not being reduced itself). The reducing agent is the reactant that is oxidized.

Describe a decomposition reaction.

A reaction in which a single compound reacts to form more than one product.

Define oxidation-reduction reaction.

A reaction in which electrons are exchanged from one substance to another, also called redox.

Describe a synthesis reaction.

A reaction in which two or more reactants combine to form one product.

What is a chemical equation, and how do scientists use these equations to represent chemical reactions?

A representation, using formulas and symbols, of a chemical reaction. It is a shorthand chemical sentence that allows us to describe the reaction without having to write a long paragraph.

How does a strong nuclear force affect matter?

A strong nuclear force is an attractive force that holds the nucleus of an atom together. It is associated with holding the protons and other subatomic particles together inside the nucleus. Protons in an atom's nucleus all have a positive charge, so they naturally repel each other due to electromagnetic forces. The strong nuclear force overrides the electromagnetic repulsion and holds the positive protons and neutral neutrons packed tightly together in an atom's nucleus. This is the strongest of the four fundamental forces, but has a very short range that does not reach far beyond an atom's nucleus.

What is a single replacement (displacement) reaction?

A type of reaction in which one element replaces a similar element within a compound.

What is a double replacement (displacement) reaction?

A type of reaction in which the ions of two compounds exchange places in an aqueous solution to form two new compounds.

The model for a double replacement reaction

AB + CD → AD + CB

The model for a decomposition reaction:

AB → A + B.

Describe why the half-life graph is curved.

According to the graph, the amount of time it takes for only half of an original sample to remain is equal to the amount it takes for the radioactive sample to decrease from one-half to one-quarter of the original amount.

What are the rules for assigning oxidation numbers? For all elements?

All the oxidation numbers (multiplied by each of their subscripts) in a compound must add up to the total charge of that compound or ion. This means we can use subtraction to solve for any elements not listed in the previous oxidation number rules.

Alpha radiation

Alpha radiation is made up of a stream of alpha particles, alpha particles are made up of two protons and two neutrons released from the nucleus of the radioactive atom. Alpha particles have a positive charge, and that when an atom releases an alpha particle, its atomic number decreases by two and its mass number decreases by four. Alpha have a high amount of kinetic energy and can cause damage to surface materials such as skin and living tissue. However, alpha particles are relatively easy to shield against. They cannot normally penetrate lightweight materials such as paper or fabric. Also, as they travel through the air, the particles attract electrons and become neutral helium atoms.

What is an application of a double replacement reaction?

An application of a double displacement reaction is seen during the neutralization of an acid using a base. This is also called an acid-base reaction.

Nuclear fission

An atom of uranium may break apart into two smaller atoms. When this happens, the resulting atoms are actually less massive in total than the original uranium atoms.

Define combustion reaction.

Any reaction in which a substance reacts with oxygen gas.

Describe atoms with unstable nuclei.

Atoms with unstable nuclei are radioactive; their nuclei eventually break down to form a different substance and release radiation in the process.

What is the advantage of conducting double replacement reactions in aqueous solutions?

Because the reactants are dissolved in water, they can move and collide together to form new products. One of the products formed is typically a solid (precipitate), a gas (bubbles), or water. The other product usually dissolved in the solution.

Beta radiation

Beta radiation is made up of a stream of beta particles. Beta particles are fast-moving electrons released from a nucleus when a neutron breaks apart into one proton and one electron. When the negative beta particle is released from the nucleus of an atom, the atom ends up with one more proton and one less neutron. Beta particles have a negative charge and they usually move faster than alpha particles. This means that beta particles are more difficult to protect against than alpha particles; they can penetrate cloth and paper. Beta particles can penetrate deeply into skin and potentially harm or kill living cells. However, these particles cannot penetrate thin layers of denser materials such as aluminum and other metals. When beta particles are finally stopped by a substance, they are absorbed by the material, like any other electron.

How do scientists use radioactive decay for carbon-14 dating?

By determining how much carbon-14 has already decayed in the artifact, chemists can estimate the age of the time.

How are changes of state different from chemical change?

Changes of state are physical changes, it doesn't change the actual chemical make-up of the substance.

Combustion reactions can also be what kind of reactions?

Combustion reactions can also be synthesis reactions, which is the combining of reactants to make one product.

What type of chemical reactions can also be redox reactions, but not always?

Combustion, synthesis, single replacement, and decomposition.

six tips to help you make sure an equation is balanced.

Count up the number of atoms for each element. Balance each element one at a time. Adding a number in front of a compound affects the number of each element in that compound. Check how this new coefficient affects each element. Sometimes an element is found in more than one compound on the same side of an equation. Try balancing the other elements first. Balancing equations is a puzzle. Use a pencil because you may have to change a coefficient more than once. If a polyatomic ion appears on both sides of the equation, balance the ion as a single unit. Double check that every element is balanced on both sides of the equation.

Insoluble product

Double replacement reactions form a product that is insoluble in water, but it bubbles out of the solution as a gas instead of forming a solid precipitate.

How can covalent bonds be part of a redox reaction?

Elements that are covalently bonded can be "oxidized" if they have less control over their electrons than before their "oxidation." The same goes for reduction, except they have more control of their electrons after "reduction."

What do we assign in a covalent molecule for redox reactions?

Even though the atoms involved in a covalent molecule do not have charges like an ion, we assign them positive and negative oxidation numbers to represent this "uneven sharing" that occurs.

What are the rules for assigning oxidation numbers? For covalent compounds?

For covalent compounds, pretend the compound is ionic with the more electronegative element forming the negative ion (anion). Fluorine is always −1 in a compound, oxygen is almost always −2, and hydrogen is +1 in covalent compounds.

List times when an element is reduced.

Gained electrons, acting in the reactant that is the oxidizing agent, has a decrease in its oxidation number.

Gamma radiation

Gamma radiation can be given off during different types of nuclear decay. Gamma rays are a form of electromagnetic waves with a very high frequency and greater energy than ultraviolet light or X-rays. Because gamma rays have high energy and no mass or charge, they can penetrate through most materials. Gamma rays can cause much more damage to living cells than alpha or beta particles. Only very dense materials, such as thick layers of lead, can stop gamma rays. This is why lead is commonly used as a shielding material in laboratories and hospitals where gamma radiation is present.

How does gravity affect matter?

Gravity is the weakest of the four fundamental forces. It has a large range. Gravity is the force of attraction that pulls objects toward the center of Earth and that holds the moon in orbit around Earth. Greater masses attract with more gravitational force, but gravitational force weakens as objects get farther apart. The combination of your mass and the gravitational force on Earth results in your weight. Since the moon is much smaller than Earth and has less mass, it has a weaker gravitational force. This weaker force means your weight would only be one sixth what it is here on Earth.

What are the four fundamental forces?

Gravity, electromagnetism, strong nuclear force, and weak nuclear force.

What factors are necessary for a chemical change to take place?

If two or more elements or chemical compounds come into contact with one another and there is enough energy present.

How does the law of conservation of mass also apply to physical changes?

If you melt a piece of ice, the mass of the liquid water is going to be the same as the mass of the ice.

In a chemical reaction, atoms cannot be _______ or _________, just rearranged.

In a chemical reaction, atoms cannot be created or destroyed, just rearranged.

Describe characteristics of combustion reactions.

In a combustion reaction, a compound or element reacts with oxygen, releasing a large amount of energy in the form of light and heat. Combustion reactions are exothermic,which means energy is released by the reaction.

Explain how a double replacement reaction cannot be a redox reaction.

In a double replacement reaction, ions do not change their charges. They do not follow the pattern of redox reactions

Describe the nature of the reactants and products in a double replacement reaction.

In a double replacement reaction, the reactants are always two compounds, and the products are always two different compounds.

Explain how a single replacement reaction can also be a redox reaction.

It involves a neutral element that changes its electrostatic charge to combine with a new compound.

Disadvantages of nuclear fission

It is difficult to initiate and control. To make it work, nuclear engineers must overcome strong repulsion forces between nuclei using extremely high temperatures that are difficult to maintain.

Nuclear fusion

It is possible to make the nuclei of two hydrogen atoms join together to form one helium nucleus. This requires that the nuclei be hurled at each other at a very high speed. This process occurs in the sun, but it can possibly be replicated on Earth with the use of lasers or magnets, or in the center of an atomic bomb. The process is called nuclear fusion.

List times when an element is oxidized.

It loses electrons, Acts in the reactant that is the reducing agent, has an increase in its oxidation number.

What do decomposition reactions need in order to occur?

It requires energy, usually in the form of heat or electricity, for the reaction to occur.

List observations from the half-life graph. What information can you learn from the graph?

It takes the same amount of time from the first interval to the second and so on. It is exponential.

How do balanced equations demonstrate the conservation of mass?

Mass is neither created or destroyed, the mass of the reactants equals the mass of the products.

What is always a reactant in combustion reactions, and what are the two types?

Molecular oxygen (O2) Organic compounds Or Inorganic compounds

What are the rules for assigning oxidation numbers? For Monatomic ions?

Monatomic ions have an oxidation number equal to their charge as an ion (when alone or in a compound)

What are the rules for assigning oxidation numbers? For neutral elements?

Neutral elements by themselves (not in a compound) will always have an oxidation number of 0.

Describe combustion with inorganic compounds.

Not all combustion reactions involve organic compounds made of carbon and hydrogen, which means the products are not always carbon dioxide and water. Other substances, both compounds and elements, can burn in oxygen. These reactions can often be categorized as synthesis reactions, but they are considered combustion reactions as well because a substance is reacting with oxygen and releasing energy. 4Fe + 3O2 → 2Fe2O3

What is true about redox?

Not all oxidation-reduction reactions form ionic bonds.

What are the two memory tools used to remember the meaning of the terms oxidation and reduction?

OIL RIG: Oxidation Is Loss (of electrons) Reduction Is Gain (of electrons) LEO the lion says GER: Losing Electrons is Oxidation Gaining Electrons is Reduction

What are some characteristics of single replacement reactions?

One element replaces another element in a compound to form a new substance. Single replacement reactions have the same number of reactants as products.

Explain the oxidation and reduction reactions that occur in a battery.

One substance gains electrons, is reduced, while the other is oxidized and loses electrons. This movement of electrons creates an electric current that can power a device.

Describe combustion with organic compounds.

Organic compounds are compounds that contain carbon covalently bonded with other elements. When a hydrocarbon (a compound containing carbon and hydrogen only) combusts, the products are usually carbon dioxide and water. The burning of propane is one example of hydrocarbon combustion. Another common combustion reaction takes place inside the cells of your body. This reaction involves the combustion of an organic compound, glucose, made of carbon, hydrogen, and oxygen. Cells combine glucose from food with oxygen to release energy.

What are the rules for assigning oxidation numbers? For oxygen?

Oxygen, when in a compound, always has an oxidation number of -2, with the exception of peroxides when it is -1.

Describe some examples of important redox reactions in our world.

Photosynthesis The human body Batteries Rusting

What is an application of radiation?

Radiation therapy to kill cancerous tissue in patients.

How does uranium decay (transmutate)?

Radioactive uranium-238 goes through alpha decay, producing an alpha particle (made of two protons and two neutrons) and leaving behind an atom of thorium-234. When this nuclear reaction occurs, energy is released in the kinetic energy of the alpha particle as well as in the form of gamma radiation. The atomic number of uranium decreases by two, and the mass number decreases by four because of the two lost protons and two lost neutrons.

What are redox reactions?

Reactions that involve the transfer of electrons

Describe how redox reactions always occur.

Redox reactions always occur together; if one reactant in a chemical reaction is oxidized, then another reactant must be reduced.

What happens during reduction? Provide an example.

Reduction is when a substance against one more electron during a reaction, therefore attaining a lower, more negative oxidation number. In the reaction of sodium and chlorine, neutral chlorine got reduced when it gained electrons from the sodium. This decreased the initial charge of zero to -1 to make a negative Cl- ion.

Molecular product

Some double replacement reactions can form a molecular product. An example of a double replacement reaction forms water as one of its products. In this reaction, hydrochloric acid (HCl) reacts with an aqueous solution of sodium hydroxide (NaOH) to form an aqueous solution of sodium chloride (NaCl) and water.

Calculating the "missing mass"

The "missing" mass was converted to energy according to Einstein's formula E = mc2. Multiplying the lost mass by the speed of light squared determines the amount of energy given off by each uranium atom as it splits.

What is transmutation

The changing of one element into another by radioactive decay.

What is radioactivity, and what are some of its sources?

The emission of radiation caused by the spontaneous disintegration of atomic nuclei. Sources: The sun, the human body, rocks and minerals, and radon.

Describe the half-life for an isotope.

The half-life of a given isotope is constant and is independent of the number of atoms in the sample.

Describe the law of conservation of mass.

The law that explains that mass cannot be created or destroyed within a closed system. Mass is neither created nor destroyed during an ordinary chemical reaction. The original atoms are still present in the product, just rearranged.

What is the only pattern for redox reactions?

The losing and gaining of electrons

What happens to the elements of a covalent bond due to the unequal sharing of electrons?

The more electronegative element becomes more "negative" and the less electronegative element becomes more "positive."

What is electrolysis?

The process in which an electric current is used to decompose a substance.

Describe the nature of the reactants and products in a single replacement reaction.

The reactants in a single replacement reaction are always an element and a compound, and the products are a different element and a different compound.

How does electromagnetism affect matter?

The second strongest force, they are the only forces that can both attract and repel each other, depending on the charges. Electromagnetic force has a very long range, but cannot reach as long as gravity's attraction. Electricity, magnetism, static, light, the electromagnetic spectrum, and the bonds and attractions between atoms, ions, and molecules are all examples of electromagnetic forces. Electromagnetic force attracts negative electrons to the positive nucleus of an atom and underlies the interactions between atoms and molecules.

. Explain what the subscripts of the reactants and products represent.

The subscripts show the phases of each substance. S: Solid L: Liquid G: Gas Aq: Aqueous Solution (a solution in which the solvent is water)

What is a half-life?

The time it takes for the radioactivity level of an isotope to decrease to half its original value. The half-life is the time needed for half of the radioactive atoms in a sample to decay.

Explain why the chemical formula below is "balanced." 2Cu + O2 → 2CuO

There are 2 Cu in the reactant and there are 2 Cu in the product. There are 2 O in the reactant and 2 O in the product.

Why are transition metals often part of redox reactions?

They can exist as ions with a variety of different charges.

How do scientists measure long half-lives?

They measure the rate of the isotope's decay using a radiation detector, the faster a substance decays, the shorter the half-life of a given isotope.

E=MC2

This formula shows the relationship between mass and energy. In both fusion and fission (unlike chemical reactions) mass is not conserved but turned into energy. Just a small loss of mass can result in a lot of energy.

Why do scientists use an activity series to determine if a single replacement reaction will occur?

To predict whether a single replacement reaction will occur. An activity series lists the elements in order of reactivity. In a single replacement reaction, a reaction will occur if the replacement element is more reactive (higher on the activity list) than the element it is trying to replace.

How does weak nuclear force affect matter?

Weak nuclear force is still very strong, but not as strong as a strong nuclear force. Responsible for different types of particle decay and radioactivity. Radioactivity occurs when the nucleus of an unstable atom breaks down, releasing charged particles and energy. Unlike gravity and electromagnetism, a weak nuclear force has a very short range. You must be near the unstable atoms to be affected.

Describe what happens during a nucleus decay.

When a radioactive element's nucleus decays, the number of protons and neutrons inside the nucleus changes. When this happens, the atom becomes another element.

What happens during oxidation? Provide an example.

When a substance loses one or more electrons during a reaction, therefore attaining a higher, more positive oxidation number. In the reaction of sodium and chlorine, neutral sodium was oxidized when it lost an electron to chlorine. This increased the initial charge of zero to +1 to make a positive Na+ ion.

Calculating the energy and mass during nuclear fusion

When the two nuclei combine, the new nucleus has less mass than the two single, separate nuclei. When the nuclei are forced together, this extra mass is released as energy. The amount of energy released can be predicted using Einstein's famous formula E = mc2.

How does thorium decay?

When thorium-234 decays, it produces a beta particle (an electron) and leaves behind an atom of protactinium-234.

What happens during electron sharing?

When two nonmetals compete for the electrons that are "shared" in a covalent bond, the electrons spend more of their time closer to the more electronegative element.

What are oxidation numbers?

a number assigned to an atom of an element that represents the number of electrons lost or gained

What are the three distinct types of radiation?

alpha beta gamma

Solid precipitate

clear aqueous solutions of lead nitrate (Pb(NO3)2) and potassium iodide (KI) combine. When one of the products of a double replacement reaction is not very soluble in water, it will not stay dissolved in the aqueous solution. The reaction produces a bright yellow solid precipitate, lead iodide (PbI2), and a clear aqueous solution of potassium nitrate (KNO3).