unit 8 chemical reactions and stoichiometry

7 evidence of chemical reaction

unexpected color change, energy gets cold or hot, odor changes, solid is formed unexpectedly, gas produced ( bubbles), irreversible process, new properties

solid

s

liquid

l

gas

g

aqueous

aq

what is a catalyst

a substance formed or process that speeds up the reaction. its written above the yields arrow

how to balance a chemical equation

1. put the inventory straight down under the arrow

2. make odd even if possible

3. how many atoms on each side

4. look at each individual element

5. you can never take away atoms.

synthesis (combination) reaction

happens when 2 or more substances react to form a single product.

balancing hint- least common multiple.

decomposition reaction

a single compound broken into 2 or more products. most require energy to occur.

balancing hint- least common multiple

combustion reaction

oxygen reacts with a substance to release energy, some are also synthesis reactions

balancing hint- least common multiple.

most are reactions with hydrocarbons- combustion method

single replacement reaction

an element replaces one part of a compound

balancing hint- keep polyatomic ions together and balance as a unit

double replacement reaction

exchange between ions between two compounds, no change in charges, may end with a precipitate

balancing hint- keep polyatomic ions together and balance as a unit.

what is the arrow pointing at in a chemical equation

the is the yields arrow it points at what is being made

what are the reactants in a chemical equation

the reactants are what is before the arrow that points at the making

what is the biggest role for when you have a combustion reaction

always check if there is an H and if its an H it will be a regular combustion reaction but if it has an H it will be a hydrocombustion reaction you always start with balancing the H’s and if the number you balance with is an odd then you have to double the other side then you move on to your C’s

what way can the yield arrow go in a chemical equation

a yield arrow can go any way so be careful how its set up

what are general examples of catalysts

usually heat,light,aqueous solution

what will heat be written as?

heat will usually be written as a triangle with no coloring in it also does not have to be a substance

what can a synthesis also be

a synthesis can also be a combustion but watch out for when it is because if it has an H use the combustion method but if no H you can stick to a normal synthesis method

what is one way to remember what the difference is between a synthesis reaction and a decomposition reaction?

they are complete opposites a synthesis will always be adding the 2 or more substances to make one product. When you have a decomposition reaction they are separating a single compound to create multiple products

stoichiometric step

the one step of dimensional analysis that converts the moles based on the reaction ratio that apply to the problem—— one step you can only use it once!!

keys to stoichiometry

know when to use the reaction. * with moles on top of dimensional analysis

know what you need to take from the reaction * one mole ratio

know how many times you take from the reaction * one time. (you cant rob the same bank 2)

limiting reactant

it stops the reaction all calculations start with a limiting reactant once it is identified

solving method

calculate the final mass of a product from both reactant and quantities and determine which is the limiting based on the least amount of product

limiting reactant

the lesser quanity calcualted is the actual amount that can be formed from the limiting reactant

excess reactant

the greater quantiy calculated is used for comparison only and this value is never produced because it is based on the excess reactant