6 and 7 Flashcards
Definition of exothermic
when energy is lost from the system to the surroundings, in form of heat and is shown in the rise of temperature in the surroundings
definition of endothermic
takes in energy from surroundings to system, in form of heat and is shown in the fall of temperature in the surroundings
exothermic
energy in reactants ? products
bonds: broken ? made
ΔH = +/- ve
Energy in reactants > products
- products have less chemical energy than the reactants
- overall the temperature increases as energy is lost to the surroundings
E: reactant ➝ surroundings
bonds: broken < made
Bond MAKING
ΔH (enthalpy - heat content in the system) = -ve for exothermic as energy is lost
endothermic
energy in reactants ? products
bonds: broken ? made
ΔH = +/- ve
Energy in reactants < products
- overall the temperature decreases
E: surroundings ➝ reactants
Bond BREAKING
ΔH (enthalpy - heat content in the system) = +ve for endothermic as energy is gained
Give 3 examples of exothermic reaction
- combustion
- neutralisation
- most oxidation reactions
- rusting iron
Give examples of exothermic reaction
- thermal decomposition
- reaction of citric acid and sodium hydrogencarbonate
- photosynthesis
definition of a catalyst
- a substance that speeds up the rate of reaction
- remains chemically unchanged
- by providing an alternative route with a lower activation energy
energy change equation
break - make
\+ve = endothermic -ve = exothermic
complete combustion reaction
excess of oxygen
hydrocarbon/fuel + O2 -> CO2 + H2O
incomplete combustion reaction
oxygen deficient environment
hydrocarbon/fuel + O2 -> CO + H2O
activation energy
minimum amount of energy needed to break bonds in reactants and start the reaction
rate of reaction definition + formula
how fast the reactants are changed into products
amount of reactant used or formed/time
enzyme definition
biological catalyst (fermentation reaction)
photochemical reactions examples
started by energy in the form of light
substitution reaction of hydrocarbons with chlorine
photographic negatives
photosynthesis
photosynthesis reaction
carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2 + energy
(light)
energy absorbed by chlorophyll
photographic negatives
AgCl -(light)-> Ag + Cl
redox reaction definition
in terms of electron transfer, a redox reaction is a reaction in which electrons move from oxidised species to reduced species
oxidising/reducing agent
oxidising agent oxidises another substances during a redox reaction - the one which is reduced, gains e-
acidified potassium manganate (VII)
KMnO4 oxidising agent
MnO4 - ion is reduced to Mn2+
- purple to colourless
- oxidation state of manganese changes from +7 to +2
potassium iodide
KI reducing agent
I- ions oxidised to iodine molecules, I2
- colourless to brown
- oxidation state of iodine changes from -1 to 0
oxidation and reduction
OILRIG
o - loss of e, gain of oxygen
r - gain of e, loss of oxygen
equilibrium
when forward and backward reaction in a reversible reaction are going at exactly same rate.
le Chatelier’s principle
when a change is made to conditions of a system at equilibrium, system automatically moves to oppose the change.
higher temperature =
equilibrium moves in endothermic direction
higher pressure
equilibrium moves in direction that produces the smallest amount of molecules of gas.
higher concentration
to favour opposite
recycling definition
process of converting waste materials into new products
+ and - to metal recycling
+: less energy (cheaper), conserves finite amount of each metal, saves costs of mining and extracting, less waste sent to landfill
-: sorted and separated = time and money
energy to collect, transport, recycle (still less)
