Module 2 Flashcards
What are atoms made up of?
Charged particles
What do chemical bonds store?
Electrostatic potential energy
What happens in an exothermic reaction?
The reaction releases heat
When does and exothermic reaction occur?
When the products have a lower heat content than the reactants
What happens in an endothermic reaction?
The reaction absorbs heat
When does an endothermic reaction occur?
When the product have a higher heat content than the reactants
What are heat changes under atmospheric pressure called?
Enthalpy
What is meant bye enthalpy is a state function?
The enthalpy of A>B will be the same regardless if it occurs in one step or a number of steps
What does a formation reaction describe?
The formation of 1 mole of a compound from its constituent elements in their standard states
What is a spontaneous process?
One which, once started, will continue without any help (energy input)
What is considered in spontaneity?
Enthalpy and entropy
What is entropy?
A measure of the number of possible arrangements of particles in a system
What does the third law of thermodynamics state?
At absolute zero, the entropy of a perfectly ordered pure crystalline substance is zero
Why is the third law of thermodynamics true?
Because there is no temperature so there can be no disorder at all
What has the lowest entropies?
Solids, followed by liquids and gases
What is likely to have a positive change in entropy?
A reaction which results in the formation of gas from a solid or liquid
What is likely to have a negative change in entropy?
A reaction which has fewer moles of products than reactants
What does it mean when change in G is negative?
The process is spontaneous
What does it mean when change in G is zero?
The system is at equilibrium
What does it mean when change in G is positive?
The process is non-spontaneous
What does the magnitude of G tell us?
How far a spontaneous reaction will go to completion
What happens when the change in H and change in S is positive?
It is spontaneous at high temperatures and non-spontaneous at low temperatures
What happens when change in H is positive and change in S is negative?
It is non-spontaneous at all temperatures
What happens when then change in H is negative and the change in S is positive?
It is spontaneous at all temperatures
What happens when the change in H and change in S is negative?
It is non-spontaneous at high temperatures and spontaneous at low temperatures
What is change in G standard important for?
Determining the position of equilibrium in a chemical system
What can a spontaneous reaction be used for?
Driving a non-spontaneous reaction by coupling them together
What are two important things about a chemical reaction?
How far it goes (thermodynamics) and how fast it goes (kinetics)
What affects the reaction rate?
Chemical nature of the reaction, physical states of reactants and products, concentration of reactants, temperature and sometimes substances not involved in the stoichiometric equation (catalysts and inhibitors)
How can concentration affect a reaction?
By increasing the rate or not affecting it at all. It depends on how the rate depends on concentration
What does the rate law describe?
How the rate depends on concentration
How is the rate law determined?
Experimentally
When is the order of something 0?
When if the concentration doubles there is no effect on the rate
When is the order of something 1?
When if the concentration doubles the rate also doubles
When is the order of something 2?
When if the concentration doubles the rate increases by 4 times
What does the units of k depend on?
The overall order of a reaction (x+y)
What is the unit of K when the order of the reaction is 0?
Mol L-1 s-1
What is the unit of K when the order of the reaction is 1?
s-1
What is the unit of K when the order of the reaction is 2?
L mol-1 s-1
What is the unit of K when the order of the reaction is 3?
L2 mol-2 s-1
How are rate of reaction and time related?
Inversely
If a reaction is twice as long the rate is…
Half as fast
What is the isolation method based on?
The initial rates of a reaction
What is done in the isolation method?
The concentration of one reactant is varied while others are held constant
What is half life?
The time taken for the concentration of a reactant to reach half its initial value
What are elementary reactions?
The series of steps which combine to give the overall reaction
What are reaction intermediates?
Species which play a role in the reaction but do not appear in the overall reaction
When is writing rate laws from stoichiometric coefficients allowed?
For elementary reactions
What is the rate determining step?
The elementary step in a reaction mechanism that is considered slower than any other step. It controls the overall rate of reaction and is the bottleneck of the reaction
