enthalpy Flashcards
What is enthalpy?
The measure of heat energy in a chemical system. Sometimes thought of as the heat energy stored in bonds.
What is difference between an exothermic and endothermic system?
Exothermic: a chemical system will release heat energy to the surroundings
Endothermic: a chemical system will take heat energy from the surroundings
What is activation energy?
The minimum energy required for a reaction to take place
What are the standard conditions in chemistry?
100 kPa is standard pressure
25*c or 298K is standard pressure
1.00 mol dm-3 is standard concentration
What is the standard enthalpy change of reaction?
The enthalpy change that occurs in a reaction in molar quantities shown in a chemical equation under standard conditions.
What is the enthalpy change of formation?
The enthalpy change that occurs when ONE MOL of a compound is FORMED FROM ITS ELEMENTS under standard conditions.
What is the standard enthalpy change of combustion?
The enthalpy change that occurs in a reaction when ONE MOL of a substance reacts completely with oxygen under standard conditions.
What is the standard enthalpy change of neutralisation?
The enthalpy change that accompanies a reaction between an acid or base to form ONE mol of H2O under standard conditions.
What is the equation for energy change?
q= mCAT
What does each symbol mean in q= mCAT and what are the units for each?
q= energy change
m: mass (usually of the water/liquid/solution)
c: specific heat capacity of water, 4.18
AT: temperature change
Why may the enthalpy change of combustion not be accurate?
+ Heat loss to surroundings other than the water
+ Incomplete combustion
+ Non standard conditions
Example question: Determine the enthalpy change of reaction for the reaction
Zn (s) + CuSO4 (aq) -> Cu (s) + ZnSO4 (aq)
An excess of zinc powder is added to 50,0cm3 of 1.00 moldm-3 copper(II) sulfate.
Initial temperature: 22.5 c
Final temperature: 60.5c
How do you determine enthalpy change of reaction/combustion with energy change from q=mcAt?
energy change / mol of reactant reacted
What is the definition of enthalpy change?
Enthalpy change is the amount of heat energy that is either given our taken in from the surroundings, during a reaction, under constant pressure.
What is le chatelier’s principle?
Le Chatelier’s principle stats that when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change.
