Thermochemistry Flashcards
What is it meant by the “system” and the “surroundings”
The system consists of the molecules which are reacting and the surroundings is everything else.
What is the energy transfer that occurs in both an endothermic and exothermic reaction?
Heat transfer
What is it meant by the term “Standard states”
Standard states are the conditions in which the substance exists during standard conditions.
What is it meant by the term “Standard conditions”
Standard conditions is the condition a substance would naturally be.
What is the definition of Enthalpy of formation?
Enthalpy of formation is the energy required to produce 1 mole of product from its constituent atoms in their standard state at standard conditions.
What is the definition of Enthalpy of combustion?
The Enthalpy of combustion is the energy requires to react 1 mole of product with oxygen under standard conditions.
What is the definition of Enthalpy of vaporisation?
The Enthalpy of vaporisation is the amount of energy required to convert 1 mole of liquid to 1 mole of gas at its boiling point.
What is the definition of Enthalpy of fusion?
The Enthalpy of fusion is the energy required to convert 1 mole of solid to 1 mole of liquid state at its melting point.
What is the definition of Enthalpy of sublimation?
Enthalpy of sublimation is the amount of energy required to convert 1 mole of a solid to 1 mole of a gas in its gaseous state at the sublimation point.
How to calculate the number of moles (n) from the mass (m) and molar mass (M)?
Use the formula (n=m/M)
How to calculate the Enthalpy (^H) from the number of moles (n) and the Enthalpy change of reaction (^rH)
- Calculate number of moles from formula (n=m/M)
2. Times the number of moles by the enthalpy change of reaction.
How to calculate the amount of heat transferred?
Using the formula q=m x c x ^T
q=Amount of heat transfered
What is the definition of specific heat capacity?
The amount of heat required to increase the temperature of one gram of water by 1c
What does a high or low specific heat capacity tell us about different compounds?
Compounds with higher specific heat capacity’s are harder to heat, compounds with lower specific heat capacity’s are easier to heat.
What does the term “Entropy” mean?
Entropy describes the disorder or randomness of a system
Does Entropy increase or decrease as you go from a solid to a liquid to a gas?
It increases as there is more randomness.
Why does Entropy increase when more moles of a substance are produced?
There is more disorder therefore an increased Entropy.
What is a spontaneous reaction?
Spontaneous reactions occur by themselves without any external help such as an extra input of energy
What is a non-spontaneous reaction?
Un-spontaneous reactions can only occur by external drive such as an input of energy.
What are the features of reactions that are spontaneous?
Exothermic + Increase of Entropy
What are the features of reactions that are un-spontaneous?
Endothermic + Decrease of Entropy
Why can it be hard to decide on whether a reaction is spontaneous or not?
In the case where you have both features of spontaneous and non-spontaneous reactions.
What is hess’s law?
The total Enthalpy change during a chemical reaction is the same whether the reaction endured one step or multiple component reactions.
Define ^rH
The amount of energy or heat absorbed in a reaction.
Define ^cH
The change in energy when one mole of a reactant is reacted with oxygen in a combustion reaction under standard conditions.
Define ^fH
The change in enthalpy when one mole of a substance, under standard conditions, is formed from pure elements.
Define ^fusH
The amount of energy required to change 1 mole of a substance from a solid to a liquid at the substances melting point.
Define ^vapH
The amount of energy required to change 1 mole of a substance from a liquid to a gas at the substances boiling point.
Define ^subH
The amount of energy required to change 1 mole of a substance from a solid to a gas at the substances sublimation point.
What is the calorimeter?
The piece of equipment used to measure the heat energy absorbed or released during a reaction.
What is Calorimetry?
The science associated with determining the changes in energy of a system by measuring the heat exchanged with its surroundings.
What is “Gibbs free energy”?
The prediction of the spontaneity of a reaction. Takes into consideration both the enthalpy and entropy changes.
What is the heating curve?
A graph of temperature versus time for a substance where energy is added at a constant rate.
What is latent heat?
The heat energy that is released or absorbed in the changing of the state of a substance.
What are the typical standard conditions?
25 degrees, 298.15 K, & 101 kPa
