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