physical chemistry Flashcards
what is an endothermic reaction
1) heat energy taken in
2) positive enthalpy change
what is an exothermic reaction
1) heat energy given out
2) negative enthalpy change
how do you calculate the heat energy change from a measured temperature change
Q=mcΔT
c=4.18 for water
describe and explain the effect of changes in surface area of a solid on the rate of a reaction
higher surface area to volume ratio= higher rate of reaction
because the particles have more area to work on so there is a higher frequency of collisions
describe and explain the effect of changes in temperature on the rate of a reaction
higher temperature= higher rate of reaction
- high temperature means the particles move faster so there are MORE COLLISIONS.
- high temperature increases the energy of the collisions since the particles are moving faster
- reactions only happen if the particles collide with enough energy
- so at a higher temperature, there are more SUCCESSFUL COLLISIONS
describe and explain the effect of changes concentration on the rate of a reaction
higher concentration/ pressure = higher rate of reaction
- higher concentration means there are more particles of a reactant in the same volume so collisions are more likely
- higher pressure in a gas means the that the particles are more crowded so there are more frequent collisions
define catalyst
a substance which speeds up the rate of reaction without being used up itself
how does a catalyst work
provides an alternate pathway with a lower activation energy
is bond breaking exothermic or endothermic
endothermic
is bond forming exothermic or endothermic
exothermic: releases energy
Is bond breaking exo or endothermic
Endothermic- positive enthalpy change
Is bond making exo or endothermic
Exothermic (negative enthalpy change)
Describe the thermal decomposition of ammonium chloride
Ammonium chloride (white solid) is broken down into ammonia gas and HCL gas (forward reaction) If it cools, ammonia and HCL react to form ammonium chloride solid (backward reaction)
Describe the dehydration of copper Sulfate
Heat blue hydrated copper Sulfate to make white anhydrous copper Sulfate
Reversible reaction
What are the characteristics of dynamic equilibrium
- the forward and reverse reactions occur at the same rate
* the concentrations of reactants and products remain constant.
why does a catalyst not affect the position of equilibrium in a reversible reaction
It speeds up the forward and backward reaction by the same amount
Describe the effect of changing temperature on the position of equilibrium in a reversible reaction:
• an increase (or decrease) in temperature shifts the position of equilibrium in the direction of the endothermic (or exothermic) reaction
Increase temperature= increase endothermic reaction
Decrease temperature= increase exothermic reaction
Describe the effect of changing pressure on the position of equilibrium
Raise the pressure; increase in the reaction which produces less moles
Lower the pressure; increase in the reaction which produces less moles
what is electrolysis
Electrolysis is a process in which electrical energy, from a direct current (dc) supply, breaks down electrolytes
what is an electrolyte
molten or dissolved ionic compounds
what is the cathode
negative electrode
what is the anode
positive electrode
what are electrodes made out of
an inert material, eg graphite or platinum
describe how to set up an electrochemical cell
1) get two inert electrodes
2) clean the surfaces of the electrodes using emery paper
3) place both electrodes into a beaker filled with the 4)electrolyte
5) connect the electrodes to a power supply using crocodile clips and wires
in the electrolysis of aqueous solutions what ions are present at the cathode/anode
cathode: H+ and metal ions
anode: OH- and halide ions
when is H2 gas formed at the cathode (in the electrolysis of aqueous solutions)
if the metal is more reactive than hydrogen ( Fe, Zn, Al, Mg, Ca, Li, Na, K)
when is Oxygen formed at the anode (in the electrolysis of aqueous solutions)
if no halide ions are present
what is the half equation for the formation of oxygen from OH ions
4OH- -> O2 + 2H2O + 4e-
or (2H2O -> 4H+ O2 + 4e-)
