Unit 3 Flashcards
What is the mole equation?
1 mole = 6.02 x 1023
What is Avogadro’s Number?
The number of particles in 1 mole of a substance
What is amount (n)?
The quantity of a substance in moles
What is the most important equation of this unit?
What is the equation to convert number of moles to number of particles and vice versa?
What is Avogadro’s constant?
What is the law of definite proportions?
A chemical compound always contains the same proportions of elements by mass
What is percentage composition?
The percent by mass of each element in a compound
How do you find percentage composition?
Add the mass percents of all the elements in the compound (should add to 100%)
What is mass percent?
The mass of an element in a compound, expressed as a percentage of the total mass of the compound
How do you find mass percent of each element in a compound?
Divide the mass of each element by the total mass of the compound and multiply by 100
How do you determine percentage composition from a chemical formula?
Divide the molar mass of each element by the molar mass of the entire compound and multiply by 100
What are the steps to finding the molecular formula?
1) Determine the empirical formula
2) Find the molar mass of the empirical formula
3) Divide the actual molar mass by the empirical formula molar mass - this gives you the multiplication factor “X”
4) Multiply the subscripts of the empirical formula by this factor “X”
What is stoichiometry?
The study of quantitive relationships among the amounts of reactants and products in a chemical reaction
What is a mole ratio?
The ratio of the amounts (in moles) of any two substances in a balanced chemical equation
*IN A BALANCED EQUATION THE COEFFICIENTS INDICATE THE NUMBER OF MOLES*
What are the steps to solving stoichiometry questions?
1) Write out the balanced chemical equation
2) Check and check again to make sure it’s balanced
3) Write the information given in the question under each reactant/product in the equation
4) Understand what is being asked by the question (is it grams or moles?)
5) Convert grams to moles
6) Use a mole ratio to find moles where needed
7) If needed, convert moles back into grams
8) Double check your calculations
What are stoichiometric amounts?
When the amounts of reactants present is the same proportion as the coefficients in the balanced chemical equation
What is a limiting reagent?
A reactant that is completely used up during a reaction - it limits how much product is made as once it runs out, the reaction stops
What is an excess reactant?
A reactant that remains after a reaction is over
What do we use to determine how many moles of a product is made?
Moles of limiting reagent
What is theoritcal yield?
The amount of product predicted by stoichiometric calculations
What is actual yield?
The actual amount of product found to be produced when you do the reaction in a lab
What is a competing reaction?
A second reaction that occurs along with the main reaction and involves the reactants and/or products of the principal reaction
What are factors that lower actual yield of a reaction?
1) Competing reaction (reactants)
2) Competing reaction (products)
3) Reaction rates
4) Reversable reaction
5) Purity of the reactants
6) Laboratory techniques
What is the collision theory?
In order for a reaction to occur, particles must collide with the proper orientation and energy
What is percentage yield?
The actual yield of a reaction expressed as a percentage of theoretical yield
What is percentage purity?
Describes what proportion by mass of a sample is composed of the actual chemical
