Enthalpy Flashcards
What is enthalpy?
The heat energy contained in chemicals (e.g. reactants or products)
What is Enthalpy change and the symbol?
The het energy change in a chemicals reactions (at constant pressure)
/\H
What is the Enthalpy of combustion and the symbol?
when 1 mole of a substance is burnt completely/in excess oxygen
C(s) + O2(g) –> CO2(g)
CH4(g) + 2O2(g) –> CO2(g) + 2H2O(l)
What is the Enthalpy of formation and the symbol?
when 1 mole of a compound is formed from its elements in their standard states
C(s) + 1/2O2(g) –> CO(g)
What is the Enthalpy of reaction and the symbol?
when reactants react in their molar ratio according to the equation
2CO(g) + O2(g) –> 2CO2(g)
CH4(g) + 3/2O2(g) –> CO(g) + 2H2O(l)
What are standard conditions?
1 atmosphere/101 kPa of pressure
25oC / 298K
What is the equation for energy change?
Energy change (J) = mass (kg) x specific heat capacity of water (J/goC) x temperature change (oC) Q = m x c x /\T c = 4.18 J/goC
What is the equation for enthalpy change?
/\H (kJ mol-1) = Q (kJ) / n
What are the limitations of measuring enthalpy change?
- reaction rate may be too slow to allow measurement of enthalpy change
- reaction may produce undesired products (isomers) instead of the one we want
What is bond enthalpy?
the enthalpy change required to break 1 mole of a covalent bond (in the gaseous phase)
What is the Enthalpy change in neutralisation?
When an acid reacts with a base (in their standard states) to produce 1 mole of water
What is the ionic equation for neutralisation?
OH- + H+ –> H2O
How do you solve the enthalpy of reaction? (m, n and /\Hr)
mass = solid + solution moles = mass of limiting/Mr of limiting /\Hr = calculates /\H x moles in equation
How do you solve the enthalpy of combustion? (m, n and /\Hr)
mass = volume of water moles = mass of fuel/Mr of fuel /\Hc = calculated /\H
How do you solve the enthalpy of neutralisation? (m, n and /\Hr)
mass = total volume of solutions
moles of limiting = cV/1000
/\Hneut = calculated /\H
