Download Ch. 6: Chemical Reactions Study Guide

Ch. 6: Chemical Reactions
Study Guide
Section 1: The Nature of Chemical Reactions
A substance that undergoes a change in a chemical reaction is a reactant.
In a chemical reaction atoms are rearranged.
A change of color is a sign that a chemical reaction is taking place.
The changes that are visible during a chemical reaction are signs that the atoms in the reactants have been rearranged.
A substance is said to be reduced when it gains electrons.
A sign that a chemical reaction is taking place is release of energy in the form of light or heat.
In a chemical reaction, atoms are rearranged, but they are not created or destroyed.
Section 2: Reaction Types
In endothermic reactions energy is transferred from the surroundings into the reactants.
An endothermic reaction is one in which heat is transferred from the surroundings to the reactants.
In an exothermic reaction, energy is transferred from the reactants to the surroundings. A chemical reaction that
transfers energy from the reactants to the surroundings is referred to as exothermic.
The energy source in photosynthesis is light energy.
A synthesis reaction is a reaction between at least two compounds in which a new, more complex compound is formed.
The product of the synthesis reaction between sodium and chlorine gas is sodium chloride.
In a decomposition reaction, the reactants are broken down into other substances.
Most of the energy in an isooctane reaction (combustion of gasoline) is released in the form of heat and light.
Digestion is an example of a decomposition reaction.
When water (H2O) is broken down by electrolysis, the products are hydrogen gas and oxygen gas.
In a combustion reaction, oxygen is used to make reactants burn.
A reaction that involves the transfer of electrons is called a redox reaction.
Section 3: Balancing Chemical Equations
A chemical equation is balanced by changing or adding coefficients. A balanced chemical equation indicates both the
number of particles of reactants and products and the number of moles. In a balanced chemical reaction, the total mass
of the products always equals the total mass of the reactants.
In the reaction 2H2O  2H2 + O2, if you start with 2 mol of water you will produce 2 moles of hydrogen gas.
In the reaction H2S + 2O2  H2SO4, the law of definite proportions predicts that for every mole of H2S you will need 2
moles of O2.
A balanced chemical equation shows the proportions of reactants and products necessary for mass to be conserved.
In the reaction 2H2O2  2H2O + O2, if you start with 4 mol of H2O2, you will end up with 2 moles of O2.
In the reaction 2Mg + O2  2MgO, the law of definite proportions states that for every 2 moles of Mg you will need one
mole of O2.
Suppose you were producing zinc chloride by the reaction Zn + 2HCl  ZnCl2 + H2. If you started with 4 moles of zinc,
you would need 8 moles of hydrogen chloride and you would produce 4 moles of zinc chloride.
Be able to balance the following chemical equations:
H2 + Cl2  2 HCl.
2 KI + Br2  2 KBr + I2
In the chemical equation CH4 + O2  CO2 + 2H2O, for every one mole of carbon dioxide you produced, you would have
2 moles of water.
In the chemical equation FeS + 2HCl  FeCl2 + H2S, the mole ratios are 1:2:1:1. In the chemical equation H2 + Cl2 
2HCl, the mole ratios are 1:1:2.