Enthalpy Flashcards
What is enthalpy?
Measure of heat energy in a chemical system
What is enthalpy change?
Enthalpy change = enthalpy of products - enthalpy of reactants
What is Hess’ Law?
An extension on the law of thermodynamics that energy cannot be created or destroyed
What is an exothermic reaction?
Heat energy is transferred from the reaction to the surroundings, enthalpy change is negative therefore energy is lost
What is an endothermic reaction?
Heat energy is transferred from the surroundings into the reaction, enthalpy change is positive therefore energy is gained
What is activation energy?
The energy required to break the bonds to start the reaction
What are standard conditions?
Standard pressure (100kPa), standard temperature (298K), standard concentration (1 mol dm-3), standard state (state in 100kPa and 298K)
What is enthalpy change of a reaction? (ΔH)
Enthalpy change that accompanies molar quantities shown in a chemical equation
What is enthalpy change of formation? (ΔfH)
Enthalpy change that takes place when one mole of a compound is formed from its elements at standard conditions
What is enthalpy change of combustion? (ΔcH)
Enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions
What is enthalpy change of neutralisation?(ΔnH)
Enthalpy change when an acid and a base react to form one mole of water; H+ (aq) + OH- (aq) -> H20 (l), = -57kJmol-1
What equation is used to calculate enthalpy change?
q = m x c x ΔT
What is the specific heat capacity of water?
4.18 Jg-1K-1
How may calculating the enthalpy change of combustion (ΔcH) be inaccurate?
Heat loss to surroundings, incomplete combustion of fuel, evaporation of fuel from wick, non-standard conditions
How is the enthalpy change of a reaction measured? (ΔrH)
Using the equation ‘q = m x c x ΔT’, a Styrofoam cup (to prevent heat loss), and a temperature to record the temperature change
