physical chemistry

Question 1

what is an endothermic reaction

Answer 1

1) heat energy taken in

2) positive enthalpy change

Question 2

what is an exothermic reaction

Answer 2

1) heat energy given out

2) negative enthalpy change

Question 3

how do you calculate the heat energy change from a measured temperature change

Answer 3

Q=mcΔT

c=4.18 for water

Question 4

describe and explain the effect of changes in surface area of a solid on the rate of a reaction

Answer 4

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

Question 5

describe and explain the effect of changes in temperature on the rate of a reaction

Answer 5

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

Question 6

describe and explain the effect of changes concentration on the rate of a reaction

Answer 6

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

Question 7

define catalyst

Answer 7

a substance which speeds up the rate of reaction without being used up itself

Question 8

how does a catalyst work

Answer 8

provides an alternate pathway with a lower activation energy

Question 9

is bond breaking exothermic or endothermic

Answer 9

endothermic

Question 10

is bond forming exothermic or endothermic

Answer 10

exothermic: releases energy

Question 11

Is bond breaking exo or endothermic

Answer 11

Endothermic- positive enthalpy change

Question 12

Is bond making exo or endothermic

Answer 12

Exothermic (negative enthalpy change)

Question 13

Describe the thermal decomposition of ammonium chloride

Answer 13

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)

Question 14

Describe the dehydration of copper Sulfate

Answer 14

Heat blue hydrated copper Sulfate to make white anhydrous copper Sulfate
Reversible reaction

Question 15

What are the characteristics of dynamic equilibrium

Answer 15

• the forward and reverse reactions occur at the same rate

* the concentrations of reactants and products remain constant.

Question 16

why does a catalyst not affect the position of equilibrium in a reversible reaction

Answer 16

It speeds up the forward and backward reaction by the same amount

Question 17

Describe the effect of changing temperature on the position of equilibrium in a reversible reaction:

Answer 17

• 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

Question 18

Describe the effect of changing pressure on the position of equilibrium

Answer 18

Raise the pressure; increase in the reaction which produces less moles
Lower the pressure; increase in the reaction which produces less moles

Question 19

what is electrolysis

Answer 19

Electrolysis is a process in which electrical energy, from a direct current (dc) supply, breaks down electrolytes

Question 20

what is an electrolyte

Answer 20

molten or dissolved ionic compounds

Question 21

what is the cathode

Answer 21

negative electrode

Question 22

what is the anode

Answer 22

positive electrode

Question 23

what are electrodes made out of

Answer 23

an inert material, eg graphite or platinum

Question 24

describe how to set up an electrochemical cell

Answer 24

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

Question 25

in the electrolysis of aqueous solutions what ions are present at the cathode/anode

Answer 25

cathode: H+ and metal ions
anode: OH- and halide ions

Question 26

when is H2 gas formed at the cathode (in the electrolysis of aqueous solutions)

Answer 26

if the metal is more reactive than hydrogen ( Fe, Zn, Al, Mg, Ca, Li, Na, K)

Question 27

when is Oxygen formed at the anode (in the electrolysis of aqueous solutions)

Answer 27

if no halide ions are present

Question 28

what is the half equation for the formation of oxygen from OH ions

Answer 28

4OH- -> O2 + 2H2O + 4e-

or (2H2O -> 4H+ O2 + 4e-)