Chemical Equations

what three key words/phrases indicate that oxygen is being used in the reaction, and therefore that you need to add it in if it isn't already told to you?

- burns in air - oxidized - combusts

what are the three steps to the general procedure for balancing equations?

1) identify the reaction 2) write an unbalanced (skeleton) equation 3) balance the equation

simplify the four steps that you need to do to write a chemical equation

1) separate the reactants from the products with an arrow, and show that reactants are being combined to each other and products are being combined to each other with a plus sign 2) use coefficients in front of each compound within the reaction to indicate how many of each are needed to balance out the compound 3) place any conditions that need to occur for the reaction to take place above the arrow (like heat or electricity, for example) 4) the physical state of each compound needs to be indicated with a letter

when writing chemical equations, it's, again, important to note your seven diatomic molecules and two additional special cases, so you're able to balance correctly. what are they, and what are the subscripts of the two special cases?

H2, N2, F2, O2, Br2, I2, Cl2 special cases: P4, S8

when balancing equations, which two specific elements and type of element should often not be balanced until the end of the equation, since they're so abundant in in many of the other compounds, and will often end up balancing themselves out anyway?

O and H - they're in so many other compounds that trying to balance them first will often screw up the other elements; and wait until the end to balance any element that's by itself, because chances are balancing the other compounds will end up affecting that one somehow anyway

what does a balanced equation contain?

a balanced equation contains the same number of each kind of atom on each side of the equation

what type of reaction do up or down arrows indicate is taking place?

a double displacement reaction

what are chemical equations?

a shorthand expression for a chemical change or reaction

which condition does a triangle represent? a squiggly line?

a triangle is often used to symbolize heat at a temperature above room temperature being supplied to the reaction, and the squiggly line is often used to symbolize that electricity is being supplied to the reaction

where are the conditions required to carry out the reaction placed?

above or below the arrow ex: 2Al + Fe2O3 -(triangle)-> 2Fe + Al3O2

what is an aqueous solution? which type of compound is most commonly found in them?

basically, the compound has been dissolved in water; acids

where can a plus sign be placed within a reaction?

between reactants and between products when needed to show that they're being combined ex: Al + Fe2O3 -> Fe + Al2O3

what do chemical reactions always involve?

change - atoms, molecules, and/or ions rearrange in chemical reactions to form new substances (and chemical equations), and bonds are also broken with new ones formed too

what do chemical equations use to represent chemical reactions?

chemical equations use chemical symbols and formulas of the reactants and products, as well as other symbolic terms, to represent a chemical reaction

where are coefficients placed within a chemical equation? what do they indicate?

coefficients are placed in front of substances to balance the equation and indicate the number of units of each substance reacting or being produced ex: 2Al + FeO3 -> 2Fe + Al2O3

there are a bunch of other conditions besides the different states of matter, heat, and electricity... name the other six.

double arrows, down arrow, up arrow, #ATM, pressure, compound

which state does g represent?

gaseous state

what does just putting the word "pressure" by a reaction mean?

it means that adding anything above 1 ATM, or normal atmospheric pressure, will set off the reaction. it's similar to #ATM, just with that one, you need a specified, certain amount of pressure, whereas with this, anything above a certain point will do

what does adding a compound, such as MNO2, mean as far as a chemical reaction goes?

it means that that compound is a catalyst to the reaction, which means it speeds it up; though the compound itself ISN'T actually going to be included in the reactants or products of the equation

what does an up arrow indicate?

it means that the reactant/product that it's next to is in a gaseous state

if there isn't a coefficient in front of a compound, what is it understood to be?

it's understood to be ONE formula unit

which state does l represent?

liquid state

does the order of your reactants on the left side of the arrow and products on the right side of the arrow matter?

no, not really. it's easier to keep track of them and double check your answers if you keep them in the same order the problem does, but as long as they're on the correct side of the arrow, it shouldn't be a problem

are states ALWAYS given in chemical equations?

nope

what two things do chemical reactions involve?

reactants and products

which four symbols are used to indicate the physical state of a particular compound within a chemical equation?

s, l, g, aq ex: 2Al (s) + Fe2O3 (s) -(triangle)-> 2Fe (l) + Al2O3 (s)

which state does s represent?

solid state

which state does aq represent?

substances in aqueous solutions

what does the down arrow mean?

that the reactant or product it's next to is a precipitate, or a solid material that's left over from a reaction that took place

what does the direction of the arrow that separates reactants and products indicate?

the direction of the reaction (whether the reactants are being combined into products or the products are being split into reactants)

reactants

the substances that are entering the reactions

products

the substances that are formed or produced in the reaction

what is the arrow often referred to as?

the yield sign

what do the two arrows on top of each other call for?

they mean the reaction is reversible, and possibly has reached chemical equilibrium, meaning that, once the reactants become products, the products turn right around and become reactants again, and it may be happening at a pace where they're both being produced at the same time

what does adding a number (most commonly 2-4) in front of ATM for a reaction mean?

well, ATM stands for atomospheric unit of pressure (we normally are at about 1 ATM on earth at sea level). it means that we need to add that amount of pressure to whatever vessel the reaction is occurring in in order for that reaction to take place

write the balanced equation for the reaction that takes place when magnesium is burned in air to produce magnesium oxide:

word equation: magnesium + oxygen -> magnesium oxide skeleton equation: Mg + O2 -> MgO balanced equation: 2Mg + O2 -> 2MgO

when methane (CH4) undergoes complete combustion, it reacts with oxygen to produce carbon dioxide and water. write a balanced equation for this reaction:

word equation: methane + oxygen -> carbon dioxide + water skeleton equation: CH4 + O2 -> CO2 + H2O balanced equation: CH4 + 2O2 -> CO2 + 2H2O

oxygen and potassium chloride are formed by heating potassium chlorate. write a balanced equation for this reaction:

word equation: potassium chlorate -(triangle)-> oxygen + potassium chloride skeleton equation: KClO3 -(triangle)-> O2 + KCl balanced equation: 2KClO3 -(triangle)-> 3O2 + 2KCl

how does one "balance the equation" when trying to balance an equation?

you use your coefficients to correctly balance the number of elements on each side ex: 2HgO -> 2Hg + O

how does one "identify the reaction" when trying to balance an equation?

you use your knowledge of chemical reactions to write a "word equation" for the reaction ex: mercury (II) oxide decomposes into mercury and oxygen mercury (II) oxide -> mercury + oxygen

how does one "write an unbalanced (skeleton) equation" when trying to balance an equation?

you use your knowledge of forming compounds to write the correct formula for each compound ex: HgO -> Hg + O2