Chemical Reactions

On this page:

  • What is a chemical equation?
  • Balancing chemical equations
  • Net ionic equations
  • Nuclear Decay 

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What is a Chemical Equation?

Chemical Equations, like the one on the left, are how you can write out a reaction. Everything on the left side of the arrow is called a reactant and everything on the right side of the arrow is called a product. 


A chemical reaction occurs when the presence of multiple chemicals under certain conditions causes a chemical change to occur. Signs that a chemical reaction has taken place include a change in color, change in smell, formation of a gas (bubbles), formation of a precipitate, or change in temperature. 

What do the numbers mean?

The large numbers (shown in blue in this example) show how many of each molecule is needed to complete the reaction. The small numbers, shown in red show how much of each element is needed to create the molecules in the products and reactants.

How to balance chemical equations

A chemical equation is balanced if the number of each element is the same in the products as the reactants. This example is balanced because there are 4 hydrogen, 2 oxygen, and 1 carbon on each side. Often, a question won't tell you how many of each molecule is in the equation (the numbers in blue are missing). Balancing equations involves figuring out how many of each molecule is needed so that each side has the same number of each element.

Net Ionic Equations

Net ionic equations simplify chemical equations by removing "spectator ions." Spectator ions are reactants that do not change form on the products side of the reaction. Identify spectator ions by looking at whether the reactants and products are aqueous, solid, liquid or gas. If two aqueous solutions are mixed, the precipitate or gas product will remain in the net ionic equation, and the ions that remain aqueous will be removed as spectator ions because they did not change form.

Example:

1. Write out chemical equation and states: NaOH (aq) + HCl (aq) --> NaCl (aq) + H2O (l)

2. Separate into ions: Na(+)(aq) + OH(-)(aq)+H(+)(aq)+Cl(-)(aq) --> Na(+)(aq)+Cl(-)(aq)+H2O(l)

3. Cancel out what matches on each side (the spectator ions): H(+)+OH(-)-->H2O

Solubility Rules

Solubility rules are important to determine if a product of a reaction will become a solid remain aqueous in solution which determines whether or not it is a spectator ion. Most important to remember are that alkali metal salts as well as nitrate and ammonium salts are soluble with few exceptions

Types of Chemical reactions

Combination/synthesis and Decomposition

Combination/synthesis and Decomposition

Combination/synthesis and Decomposition

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Combination/synthesis reactions occur when two or more atoms or molecules come together to form a single molecule following the general form A+B→C


Decomposition reactions are the opposite of synthesis reactions in that a large molecule separates into smaller ones following the general form A→B+C

Combustion

Combination/synthesis and Decomposition

Combination/synthesis and Decomposition

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Combustion reactions occur when a hydrocarbon reactions with oxygen to produce carbon dioxide and water following the general form CxHy+O2→CO2 + H2O

Single Replacement

Combination/synthesis and Decomposition

Single Replacement

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Single replacement reactions occur when an atom or molecule switches from one compound to another following the general form A+BX→B+AX

Double Replacement

Double Replacement

Single Replacement

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Double replacement reactions occur occur when two atoms or molecules replace each other in two compounds following the general form AY+BX→BY+AX

Acid Base

Double Replacement

Acid Base

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Acid base reactions occur when an acid reacts with a base, causing an exchange of H+ ions and often creating water as a product such as in a neutralization reaction. Visit the acid/base page for more information

Redox

Double Replacement

Acid Base

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Reduction/oxidation (redox) reactions occur when electrons are exchanged and the oxidation numbers of certain species change. Visit the electrochem page for more information about redox reactions

Nuclear Decay

What is Nuclear Decay?

What is Nuclear Decay?

What is Nuclear Decay?

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Nuclear decay, also known as radioactive decay, describes the process wherein an atom is transmutated into a different element. In each nuclear symbol, the bottom number represents the protons while the top number represents the mass. While the mass number of an element can change, the protons define the element and this number cannot change without changing the element symbol

Alpha Particle

What is Nuclear Decay?

What is Nuclear Decay?

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Circled in the image above is the alpha particle. The equation above details the change that takes place during alpha decay. It is important to memorize the alpha particle, as well as the other particles detailed on this page.

Neutron Particle

What is Nuclear Decay?

Positron Particle

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This equation above takes fluorine and outputs an isotope of that same element. This is due to the neutron particle that is circled above.

Positron Particle

Nuclear Decay Equations

Positron Particle

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Above is an example of positron emission. The transition from boron to carbon occurs due to the positron particle, which is circled above.

Beta/Electron Particle

Nuclear Decay Equations

Nuclear Decay Equations

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In the picture above, a reaction is shown. What is circled is the beta particle, which is the key piece of the equation. The beta particle is also known as the electron particle. 

Nuclear Decay Equations

Nuclear Decay Equations

Nuclear Decay Equations

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When completing a nuclear decay question, use any of the particles mentioned here to ensure that the top and bottom numbers are equal on both the reactants and products side of the reaction.