Thermochemistry

Question 1

Thermochemistry

Answer 1

heat changes of chemical reactions
helps to determine if a particular reaction will occur and if it will release or absorb energy as it occurs

Question 2

two principles of thermodynamics

Answer 2

Laplace law
Hess’ Law

Question 3

The Laplace Law

Answer 3

the heat change (or enthalpy change) of a chemical reaction is exactly equal but opposite in sign for the reverse reaction
∆Hforward reaction = ∆Hbackword reaction
(a) CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) [here, ∆H0 = -890.3 kJ mol-1]
(b) CO2 (g) + 2H2O (l) → CH4 (g) + 2O2 (g) [here, ∆H0 = +890.3 kJ mol-1]

Question 4

Enthalpy Notations

Answer 4

enthalpy change 𝚫H(delta H) is the heat energy transferred in a reaction at constant pressure. The units are Kj mol⁻1

Question 5

Standard conditions (𝚫Hᶿ)

Answer 5

100 kPa pressure and a stated temperature

Question 6

Energy

Answer 6

stored in the bonds of chemical compounds.
Chemical energy may be released during a chemical reaction, often in the form of heat; such reactions are called exothermic.

Question 7

Work

Answer 7

transfer of mechanical energy between two systems

Question 8

Heat

Answer 8

transfer of thermal energy between systems

Question 9

Exothermic reactions

Answer 9

have a negative enthalpy change value, because heat is given out (the chemicals lose energy)

Question 10

Endothermic reactions

Answer 10

have a positive enthalpy change value, because heat energy is absorbed (the chemicals lose energy)

Question 11

Lattice formation enthalpy

Answer 11

enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions

Question 12

Lattice dissociation enthalpy

Answer 12

enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Question 13

Bond dissociation enthalpy

Answer 13

enthalpy change when all the bonds of the same type in 1 mole of gaseous atoms are broken

Question 14

First ionisation energy

Answer 14

enthalpy change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms

Question 15

First electron affinity

Answer 15

enthalpy change when 1 mole of gaseous 1- ions are made from 1 mole of gaseous ions

Question 16

three types of thermodynamics systems

Answer 16

open
closed
isolated

Question 17

isolated system

Answer 17

thermodynamic system that cannot exchange either energy or matter outside the boundaries of the system
1. The system may be so distant from another system that it cannot interact with them.
2. The system may be enclosed such that neither energy nor mass may enter or exit.

Question 18

Closed systems

Answer 18

only closed to matter, energy can be exchanged across the system’s boundaries

Question 19

Open system

Answer 19

exchange both energy and matter with its surroundings

Question 20

Hess’ Law

Answer 20

The enthalpy change accompanying a chemical reaction is independent of the route by which the chemical reaction occurs.

Question 21

1st law of thermodynamics

Answer 21

a systems energy content remains constant as well as not being able to be created or destroyed

Question 22

Activation energy

Answer 22

minimum energy required

Question 23

Increase temp effect on Maxwell-Boltzmann diagram

Answer 23

move right

Question 24

Reaction Rate for a given chemical reaction

Answer 24

measure of the change in concentration of the reactants or the change in concentration of the products per unit time

Question 25

speed of a chemical reaction

Answer 25

change in concentration of a substance divided by the time interval during which this change is observed

Question 26

Rate formula

Answer 26

change in concentration (of products or reactants)/ time

Question 27

Reaction rate and concentration

Answer 27

increases
more of the reacting molecules or ions are present to form the reaction products
limit is often reached where increasing the concentration has little effect on the rate of reaction.
When several reactants are involved, increasing the concentration of one of them may not affect the rate of reaction if not enough of the other reactants is available

Question 28

Reaction rate and Temperature

Answer 28

increases
Particles can only react when they collide
heat a substance, the particles move faster and so collide more frequently
disproportionately large increase in the number of high energy collisions. It is only these collisions (possessing at least the activation energy for the reaction) which result in a reaction.

Question 29

Reaction rate and Surface Area + on graph

Answer 29

cutting the substance into small pieces, or by grinding it into a powder
more particles are exposed to the other reactant
there are more collisions
the rate of reaction increases

has a steeper gradient at the start
becomes horizontal sooner

Question 30

half-life of a reaction

Answer 30

amount of time needed for a reactant concentration to decrease by half compared to its initial concentration
used in chemistry and medicine to predict the concentration of a substance over time

Question 31

concepts of half life plays a key role in

Answer 31

administration of drugs into the target, especially in the elimination phase, where half life is used to determine how quickly a drug decrease in the target after it has been absorbed in the unit of time (sec, minute, day,etc.) or elimination rate constant ke (minute-1, hour-1, day-1,etc.).

Question 32

Zero order kinetics

Answer 32

rate of a reaction does not depend on the substrate concentration
slope of this plot is a straight line with negative slope
the half-life of zero order reaction decreases as the concentration decreases

Question 33

First Order Kinetics

Answer 33

slope continually decreases as time progresses until it reaches zero
the length of half-life will be constant, independent of concentration
takes the same amount of time for the concentration to decrease from one point to another point

Question 34

Second Order Reactions

Answer 34

decrease at a much faster rate
length of half-life increases while the concentration of substrate constantly decreases, unlike zero and first order reaction

Question 35

rate equation

Answer 35

rate = k [A]a [B]b

shows the effect of changing the concentrations of the reactants on the rate of the reaction

Question 36

rate constant

Answer 36

only changes if conc changes

Question 37

The Arrhenius equation

Answer 37

k = Ae ^Ea/RT

Question 38

gas constant

Answer 38

constant which comes from an equation, pV=nRT, which relates the pressure, volume and temperature of a particular number of moles of gas

Question 39

Activation energy, EA units

Answer 39

joules per mole