30 terms

Chem: Chapter 5 - chemical reactions

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chemical bond
attractive force that holds together the atoms in a molecule.
basic types are ionic, covalent and metallic
element
a pure substance made up of only one type of atom; it cannot be broken down into simpler substances
compound
a pure substance that contains atoms of two or more different elements combined in a fixed ratio.
molecule
a pure substance made up of two or more atoms which are combined in a constant ratio and held together by chemical bonds. The substance may have two of the same type of atoms or two different types of atoms.
physical change
process in which some properties of a substance change, but the substance is still the same. Liquid water freezing to ice is one example.
chemical reaction
a process in which existing bonds are broken and new bonds are formed, producing substances which are different from the starting materials.
reactant
the substance that you start with in a chemical reaction
product
the new substance that are formed in a chemical reaction
chemical equation
A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products
precipitate
a solid that forms as a result of mixing two solutions
chemical formula
A combination of element symbols which shows how many and which type of elements are in a compound.
indicator
a substance that is added to a reaction to show the presence or amount of another material, or to show the progress of a reaction (an example is an acid-base indicator like litmus paper or phenlophthalein).
catalyst
a substance that speeds up a chemical reaction, but is itself not permanently changed by the reaction.
covalent bond
chemical bond formed when two atoms share one or more electrons.
ionic bond
chemical bond formed when one atom gains and a second atom loses electrons.
single replacement
a reaction in which one element takes the place of another element in a compound
double replacement
a reaction where two reactants exchange places in ionic compounds
decomposition
a reaction where the compound breaks down to form two or more simpler substances
combination
a reaction in which two or more substances combine to form a new compound. Also called synthesis.
evidence of a chemical reaction
color change, energy change (temperature), a gas is produced (bubbling), a precipitate forms
endothermic
a reaction that absorbs energy more energy than it releases
(feels cold if touched)
exothermic
A reaction that releases more energy than it absorbs (feels hot if touched)
coefficient
regular sized numbers in front of a chemical formula that indicate how many copies of that material are present in a chemical equation
subscript
small numbers written after and to the lower right of atoms or polyatomic ions that indicate how many copies of that atom or ion are in the chemical formula
photochemical
Reactions that only take place in the presence of light. These reactions are often synthesis or decomposition reactions and depend on specific wavelengths of light to occur. Examples are the formation of ozone or smog and the decomposition of chlorine in swimming pools.
neutralization
A reaction in which an acid reacts with a base and forms water and a "salt"
salt
Ionic compounds that form from the ions left behind when an acid neutralizes a base.
HX (acid) + YOH (base) →
H⁺ + X⁻ + Y⁺ + OH⁻ (ions in solution) →
HOH (water) + XY (salt)
acid
A molecule that releases Hydrogen Ions (H⁺) when dissolved in water. These substances taste sour, react with metals and carbonates to form Hydrogen gas (H₂), and turn litmus paper red.
base
A substance that releases Hydroxide Ions (OH⁻) when dissolved in water. These substances taste bitter, feel slippery or soapy, react with oils and grease, and turn litmus paper blue.
combustion
A chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light. Reactions with hydrocarbons produce carbon dioxide and water.
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