7. Chemical reactions Flashcards
physical and chemical changes
formation of a new substance
difficult to reverse
properties different to reactant
Describe collision theory
number of particles per unit volume
frequency of collisions between particles
kinetic energy of particles
activation energy, Ea
Factors affecting rate of reaction
temperature- kinetic energy of particles increases, foc between particles increases, higher percentage of particles have energy greater than/ equal to activation energy
pressure- gas particles are pushed closer together, more particles per unit volume, more foc
concentration- more particles per unit volume so foc between particles increases
surface area- more particles exposed to reactants so more foc
adding or removing a catalyst, including enzymes
Catalyst
increases the rate of a reaction and is unchanged at the end of a reaction.
It decreases the activation energy, Ea, of a reaction. (by providing alternative pathway requiring lower AE).
mass remain same, are specific to a reaction, required in small amounts
a reversible reaction in a closed system is at equilibrium when
the rate of the forward reaction is equal to the rate of the reverse reaction
the concentrations of reactants and products are no longer changing
Effect of temperature, pressure, concentration and catalyst on equilibrium
inc temperature- endothermic direction equilibrium shifts to
inc pressure- fewer moles of gas
inc concentration- moves to right (product)
using a catalyst- does not affect
how changing the conditions can change the direction of a reversible reaction for:
(a) the effect of heat on hydrated compounds
(b) the addition of water to anhydrous compounds
add water- hydrated- exothermic- contain water of crystallization
heat- anhydrous- endothermic- dehydrated
CuSO4.5H2O reversible- white to blue
CoCl2.6H2O reversible- blue to pink
Haber process- equation, reactants, conditions
N2(g) + 3H2(g) ⇌ 2NH3(g)
CH4 (g) + H2O(g) ⇌ 3H2(g)+ CO(g)
hydrogen (methane)- steam reforming
nitrogen (liquid air)- fractional distillation
450°C, 20000kPa /200atm and an iron catalyst
CH4(g)+ H2O(l) ⇌ 3H2 (g)+ CO(g)
contact process- equation, reactants, conditions
S+ O2 → SO2
2SO2(g) + O2(g) ⇌ 2SO3(g)
(burning sulfur or roasting sulfide ores) and oxygen (air) in the Contact process
450°C, 200kPa /2atm and a
vanadium(V) oxide catalyst
Define oxidation no., redox reactions, oxidation and reduction, oxidising agent and reducing agent
Use a Roman numeral to indicate the oxidation number of an element in a compound.
involving simultaneous oxidation and reduction
oxidation- gain of oxygen, loss of electron, loss of hydrogen, inc in oxidation no.
reduction- loss of oxygen, gain of electron, gain of hydrogen, dec in oxidation no.
oxidising agent- a substance that oxidises another substance and is itself reduced
reducing agent- a substance that reduces another substance and is itself oxidised
Identify redox reactions by the colour changes involved when using acidified aqueous potassium manganate(VII) or aqueous potassium iodide
acidified potassium manganate(VII) is an oxidising agent which, when added to a reducing agent its colour changes from purple to colourless.
Potassium iodide, KI, is a reducing agent, turns from colourless to red-brown when added to an acidified solution of an oxidising agent
