1 Stoichiometry Flashcards
What are elements?
Substances made from one type of atom which cannot be broken down. They are shown in the periodic table
What are compounds?
Compounds are made of two or more elements chemically combined. The properties of the compiunds can be different from the elements that form them
Give me an example of elements that form a compound
When you join Sodium and Chlorine to form Salt.
Reactive metal + poisonous gas = consumable salt
2Na + Cl2 = NaCl
What happens in mixtures?
Elements and compounds bond with each other. However, it is a physical bond. They are not chemically bonded and retain their individual properties
What are the two types of mixtures?
- Homogeneous: uniform composition and properties (salt + water)
- Heterogeneous: non-uniform composition. It has visibly different substances (sand + water)
Name all of the state changes
6
- melting
- vaporization (evaporation & boiling)
- condensation
- deposition
- freezing (solidification)
- sublimination
- deposition
Name the three endothermic state changes
- melting
- deposition
- vaporisation
endothermic: absorbs heat from surroundings
Name the three exothermic state changes
- freezing
- condensation
- deposition
exothermic: releases heat to the surroundings
why is the conversion of solid to liquid an endothermic reaction?
Endothermic reactions are the ones absorb energy from the surroundings. The jump from solid to liquid at a molecular level makes the particles move faster (have more kinetic energy) so energy is needed to so this shift.
What is needed to break bonds?
Energy is always needed to overcome the forces of attraction between the particles. This breaking happens when there is a chenge of state (eg. solid - liquid - gas)
What happens during chemical reactions?
As atoms cannot be created or destroyed, they are redistributed during a chemical reaction. Therefore, the reaction must be balanced, there should be equal amounts of atoms in each side of a written equation.
How to calculate the percentage purity of a compound?
(mass of pure compound/ total mass of impure sample) x 100
What are moles?
Moles are a unit for measurment used to measure the amount of atoms in a particle.
As atoms are too small to count, moles are used.
What does the Avogadro’s number determine?
the number of particles that a mole has
* 6.02 x 10^23 g mol-
What is the relationship between molar mass, mass and moles?
formula
n=m/M
Determine the molar ratios in the following equation: 2H2 + O2 = 2H20
- O2:H2O - 1:2, for every mol of oxygen reacted, 2 mols of water are produced
- H2:H2O - 1:1, for every hydrogen reacted, a water molecule is produced
What are the two types of formulas?
- Molecular shows actual number of atoms (full version) C6H12O2
- Empirical shows the simplified version C3H6O
How do you find the empirical formula given the percentage composition?
- Check that the percentages sum up to 100
- Assuming that 100% = 100g, divide each percentage by its relatiove atomic mass to find the moles of each element ((n=m/M)
- divide the moles by the simplest integrer satio to get the number of atoms of each element in the empirical formula.
How do you find the molecular formila given mass and the empirical formula?
- Calculate the molecular mass of the empirical formula
- Compare it (^) with the actual mass of the compound. Find the common ratio
- Multiplu the empirical formula with this ratio
How is the percentage yield calculated?
Percentage yield= (experimental/ theoretical) x100
* Experimental yield: the yield produced in an experiement
* Theoretical yield: the yiel expected theoretically, assuming all the limiting reactant is converted into products
The yield gained in an experiment is often lower in an experiment due to errors with method
What are the limiting and excess reactants?
- Limiting reactant is completely used during the reactant
- Excess reactants are what remains after the reaction is finished
How is the limiting reactant determined?
- Convert the masses to moles
- Divide the moles by the ratio coefficients
- The reactant with the smaller number is the limiting reactant
What are gases?
Properties and two types
Gases do not have definite shape
* Ideal gases are gases without properties that interact with other molecules of gas
* Real gases are the ones found in nature with certain physical and chemical properties that are interacting with other gases (what happens in nature)
Combined gas laws
(P1 V1)/T1 = (P2 V2)/T1
* P and V are inversely proportional (curved line)
* T and V or P are directly proportional (straight line)
