Energetics Flashcards
What is the difference between and open and closed system?
An open system can exchange energy and matter with the surroundings. A closed system can exchange energy but not matter with the surroundings.
What is temperature?
Temperature is the average kinetic energy of molecules (K, kelvins)
What is heat?
Heat is the amount of energy exchanged due to a temperature difference between two substances (J, joules)
What is enthalpy
Enthalpy is the amount of energy or heat content of a substance. The energy is stored in chemical bonds. It incudes kinetic and potential energy and is not measured directly but changers are measured (J)
What is standard enthalpy change of reaction?
The difference between the enthalpy of the products and of the reactants at 298K and 1.00 x 10^5Pa
What is change in enthalpy? (Formula)
Enthalpy of products - enthalpy of reactants
What value of enthalpy do the most un-stable substance?
The higher the value of enthalpy, the less stable the substance
What are examples of exothermic reaction?
-Combustion reactions
-Neutralization reactions
Heat energy change (Q)
Q (J) = mass (g) x specific heat capacity(J g–1 K–1) x change in temp (K)
What are the standard conditions
for enthalpy changes
-100kPa
-1 mol/dm3 for all solutions
-all substances in there standard states
What is the standard state of a substance
The standard state of a substance is the pure form of the substance under standard conditions of 298 K (25 °C) and 1.00 × 10^5 Pa
What is the specific heat capacity of water?
4.18 J g–1 K–1
What is the standard enthalpy change of combustion?
The standard enthalpy change of combustion is the enthalpy change for the complete combustion of one mole of a substance in its standard state in excess oxygen under standard conditions
What are the 4 assumptions we need to make when calculating enthalpy?
1 no heat loss from the system
2 all the heat goes from the reaction to the water
3 the solution is dilute: V(CuSO4) = V(H2O)
4 water has a density of 1.00 g cm–
What is Hess’s law?
The enthalpy change for any chemical reaction is independent of the route, provided the starting conditions and final conditions, and reactants and products, are the same.
What is standard enthalpy
of formation?
The standard enthalpy of formation of a substance is the enthalpy change that occurs when one mole of the substance is formed from its elements in their standard states under standard conditions of 298 K (25 °C) and 1.00 ×10^5 Pa
∆H reaction
∆H reaction =∑∆H⊖f (products) – ∑∆H⊖f (reactants
What is average bond enthalpy?
The average bond enthalpy is the energy needed to break one mole of bonds in gaseous molecules under standard conditions averaged over similar compounds.
What is ionization energy?
The ionization energy is the minimum energy required to remove one mole of electrons from one mole of gaseous atoms.
What is electron affinity?
Electron affinity is the enthalpy change when one mole of gaseous electrons is added to one mole of gaseous atoms
What is lattice enthalpy?
The lattice enthalpy is the enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions.
What is enthalpy change
of atomization ?
The enthalpy change of atomization is the enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state
Heat capacity
The heat capacity (C) is defined as the heat needed to increase the Temperature of an object by 1 K
Specific heat capacity
The specific heat capacity (c) is defined as the heat needed to increase the temperature of unit mass of material by 1 K
How much heat is released when 10.0 g of copper with a specifc heat capacity of
0.385 J g–1 °C–1 is cooled from 85.0 °C to 25.0 °C
heat change = m × c × ∆T
= 10.0 g × 0.385 J g–1 °C–1 × –60.0 °C (the value is negative as
the Cu has lost heat)
= –231 (J)
Why is bond breaking Endothermic?
A covalent bond is due to the electrostatic attraction between the shared pair of electrons and the positive nuclei of the bonded atoms. Energy is needed to
separate the atoms in a bond.
What is Enthalpy of Solution
The enthalpy change when one mole of a solute is dissolved in a solvent to infinite dilution under standard conditions
∆Solution = ∆Lattice + ∆Hydration
What is Enthalpy change of hydration?
The Enthalpy change that occurs when one mole of gaseous ions is dissolved to form an infinitely dilute solution of one mole of aquel ions under standard conditions
What is a spontaneous reaction?
A reaction which occurs without the need to do work. A spontaneous reaction occurs without adding energy)
What is Entropy?
The available distribution of available energy among the particles
Formula for entropy change of a reaction:
Entropy of products - Entropy of reactants
Entropy of surrounding is proportional to
(Negative) Change in enthalpy
Entropy if surrounding is inverse proportional to
Temperature
Formula for entropy of surroundings
(-change in enthalpy) / temperature
When is a reaction spontaneous
When (entropy of system) - (entropy of surrounding) > 0
Formula for Gibs free energy
Change in entropy of system - (temperature [K] x entropy change of system) <0
Under what conditions is a reaction with a positive entropy of system feasible?
High temperature
Which reactions can occur at low temperature?
Combustion
How do we calculate ∆H using bond enthalpies?
Bonds Broken - Bonds Formed
