Enthalpy Flashcards
What is enthalpy?
Enthalpy H is a measure of the heat energy in a chemical system.
Enthalpy is sometimes thought of as the energy stored within bonds.
What is chemical system?
The chemical system refers to the atoms, molecules, or ions making up the chemicals.
How do you calculate the enthalpy change?
∆H = H(products) - H(reactants)
What is the law of conservation of energy?
The law of conservation of energy is one of the fundamental rules of science and states that energy cannot be created or destroyed.
Energy transfer can be in either of two directions:
From the system to the surroundings - exothermic change
From the surroundings to the system - endothermic change.
Is exothermic positive or negative energy change?
Negative
Is endothermic positive or negative energy change?
Positive
What is activation energy?
Minimum amount if energy required for a reaction to take place.
Standard enthalpy is written as:
∆H⦵
What is standard pressure?
100kPa
What is standard temperature?
298 K
What is standard concentration?
1moldm^-3
What is standard state?
Standard state is the physical state of a substance under standard conditions. The standard state is 100kPa and 298K.
What is the standard enthalpy change of a reaction?
∆rH⦵ is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.
What is the standard enthalpy change of a formation?
∆fH⦵ is the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.
What is the standard enthalpy change of a combustion?
∆cH⦵ is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states.
What is the standard enthalpy change of a neutralisation?
∆neutH⦵ is the energy change that accompanies the reaction of an acid by a base to form one mole of H2O(l), under standard conditions, with all reactants and products iin their standard states.
What is the conversion of K to temp?
Kelvin = celsius + 273
What is specific heat capacity?
energy requires the raise the temperature of 1g of a substance by 1K
How do you calculate temp change?
∆T = T(final) - T(initial)
How do you calculate heat energy (q)?
q = mc∆T
What is average bond enthalpy?
Energu required to break 1 mole of a specified tyape of bond in a gaseou molecule - energy is required to break bonds so is always endothermic
Bond breaking:
1. take in/gives out?
2. positive/negative?
3. Endo/Exo-thermic?
Energy is required to break bonds so bonds breaking so endothermic.
∆H = positive
Bond making:
1. take in/gives out?
2. positive/negative?
3. Endo/Exo-thermic?
Energy is released when bonds form bonds, so bond making is exothermic.
∆H = negatuve
