physical and chemical change Flashcards
indicators of physical change
temperature of substance increases
change in size or shape
expected colour change
conductivity of metals decreases
substance may change phase
physical change
-identity of reactants and products remains unchanged
-overcoming forces
indicators of chemical change
unexpected colour change
gas formed
heat released/absorbed
precipitate (solid) formed
light produced
chemical change
atoms,molecules,ions rearrange themselves in new patterns and ratios
breaking bonds
synthesis reaction
chemical reaction where 2 or more simple substances are combined to form a complex product
A+B—>AB
decomposition reaction
one reactant produces 2 or more products
AB—>A + B
dissolution
soluble solid is placed into water and breaks down into smaller particles surrounded by water molecules
why does dissolution occur
because of the polar nature of water
dissociation
the splitting of an ionic compound into its ions
explain process of dissociation
formation of ions from ionic compounds
any ionic soluble substance
ionic salt further breaks down into anions and cations
ions separate away from each other by attraction of water molecules for them
what is formed when ionic substances dissociate in water
electrolyte
aqueous solution that can conduct electricity as the ions are free to move to carry charge
nitrates solubility
all soluble
group 1 compounds solubility
Li+, K+, Na+, NH4+
all soluble
Halides solubility
Cl-,Br-,I- most soluble
except Ag2+, Pb2+, Hg2+
Sulphates solubility
SO4 2-
Ba2+, Pb2+,Ca2+
Carbonates
CO3 2-
most insoluble
except Li+, K+, Na+, NH4+
silver chloride (s) colour
white
lead chloride colour (s)
white
silver bromide colour (s)
Cream
lead bromide (s) colour
pale yellow
silver iodide (s) colour
pale yellow
lead iodide (s) colour
bright yellow
sulphate (s) colour
white
carbonate (s) colour
white
what is an ion exchange reaction
2 aqueous ionic solutions are mixed
cations exchange respective anions
AB (aq) + CD(aq) + AD + CB
bond energy
energy stored in a bond
energy needed to break bond
energy released when bond broken
bond distance
distance between atoms when they have bonded
when a bond is broken…
substance less stable
energy taken in
Ep increases
bond made..
substance more stable
energy released/out
Ep decreases
how can aqueous ionic solutions undergo chemical change
electrolysis
ion-exchange reactions
activation energy
the minimum energy required to start a chemical reaction OR the energy
required to form the activated complex
Ein/Ea
activated complex
a high energy, unstable, temporary transition state between the reactants
and the products
exothermic reactions
reactions which transform chemical potential energy into thermal
energy
Ereleased
net release of thermal energy
delta h<0
negative
more energy released than absorbed
surrrondings heated
bonds of product stronger than bonds of reactants
endothermic reaction
reactions which transform thermal energy into chemical potential
energy
Eenergy absorbed >Ereleaseed
positive
delta H>0
temp of surroundings decrease
bonds of reactants stronger than bonds of products
net absorption of thermal energy
ion exchange formula
cations exchanged w respective anions
AB+CD—> AD+BC
how is reaction determined endo or exo
every chemical reaction has a endothermic (bond breaks) and exothermic( bonds made) component
never same value-overall reaction
catalyst
a substance that increases the rate of the reaction but remains unchanged at the
end of the reaction
delta H
heat of reaction/change in enthalpy
net change of chemical potential energy of system
temperature
a measure of the average kinetic energy of the particles of a substance
melting point
the temperature at which a solid changes phase to a liquid
boiling point
the temperature at which a liquid changes phase to a gas
freezing point
the temperature at which a liquid changes phase to a solid
ionisation
the reaction of a molecular substance with water to produce ions
