2 Energetics and Enthalpy Changes Flashcards
What is the definition for the standard enthalpy change?
The enthalpy change that happens when one mole of a substance is completely combusted in oxygen under standard conditions
What does effervescence mean?
Bubbles a lot
What is the symbol for the standard enthalpy change of combustion?
C
When working out standard enthalpy change what are the rules?
First must be one mole
Can halve diatomic molecules
What is the definition for the standard enthalpy change of formation?
The enthalpy change when one mole of a compound is formed from its elements in their standard states
Do elements have an enthalpy change for formation?
Nope
When working out enthalpy change, what form of carbon must be used?
Graphite
C(graphite)
What is the symbol for the standard enthalpy change of formation?
f
What is the definition for the standard enthalpy change of atomisation?
The enthalpy change when one mole of its atoms in the gaseous state is formed from the element under standard conditions
What is the symbol for standard enthalpy change of atomisation?
at
Standard enthalpy changes of atomisation is and exothermic/endothermic process
Exothermic
What doesn’t have a standard enthalpy change of atomisation?
Noble gases
What is the definition of the energy change of neutralisation?
The enthalpy change of a reaction where one mole of acid is neutralised by an alkali in their standard states at 298K and in solutions containing 1moldm(3)
What is the enthalpy of neutralisation for strong acids with strong bases?
-58kJmol
What is the definition of Hess’ Law?
The enthalpy change is independent of the path taken
What happens if you the opposite way in Hess’ Law?
You subtract the value of the enthalpy change
What is ALWAYS produced as a result of combustion?
Carbon dioxide
Water
What is the equation for energy change?
Mass (g) x specific heat capacity (JK[-1]g[-1]) x temperature change (K)
What is the equation for working out standard enthalpy change?
Sum of bonds broken - sum of bonds made
Sum of enthalpy change of formation (products) - sum of enthalpy change of formation (reactants)
What is the equation for the number of moles?
Mass in g/mass of 1 mile
Volume gas dm(3)/24dm(3)
Concentration x volume
What does the term ‘enthalpy change of a reaction’ mean?
Heat energy that is released into the surroundings in an exothermic reaction
What is the definition for lattice enthalpy?
Standard enthalpy change of formation of one mole of an ionic compound from its gaseous ions under standard conditions
What is the definition for standard molar entropy change of atomisation?
The enthalpy change that takes place when one mole of gaseous atoms is formed from its elements in its standards state under standard conditions
What is the definition of electron affinity?
Energy change when one mole of gaseous atoms acquire one mole of electrons to form a single negatively charged ion
What is energetics?
Study on energy transfers between reacting chemicals and surroundings
Does breaking bonds will require energy or release energy?
Require
Does making bonds require or release energy?
Release
Give an example of an exothermic reaction and an endothermic reaction
Exothermic – neutralisation
Endothermic – photosynthesis
What is the definition for enthalpy change of reaction?
Exothermic reaction releases energy to the surroundings in the form of heat
What is the system?
The reaction in which the changes are happening brackets products and reactants
What is meant by the surroundings?
Outside the system
What are the two sorts of boundaries and what do they prevent?
Closed prevents particles entering/leaving system
Isolated prevents particles and energy entering/leaving system
What is the first law of thermodynamics?
Energy cannot be created or destroyed
What happens to the energy transferred to surroundings?
Dissipated
What is the principle of conservation energy?
The total energy content of the universe is constant
What is the equation to work out the enthalpy change of a reaction
What is the enthalpy change of an exothermic reaction?
Negative
H(products)< H(reactants)
Net decrease in potential energy of the system
What is the enthalpy change of an endothermic reaction?
Positive
H(products)> H(reactants)
Net increase in potential energy of the system
What does the enthalpy level diagram of an exothermic reaction look like?
_______
|______
What does the enthalpy level diagram of an endothermic reaction look like?
_____
____|
What is thermochemistry?
The study of the quantities of heat during reactions
What does enthalpy mean?
The energy content of the system held at constant pressure
Represented by H
