F322-Enthalpy Flashcards
What would happen to the temperature of the surroundings in an exothermic reaction?
It would rise
Define exothermic
Heat is given out to the surroundings (reactants lose energy)
Which direction does Delta H go on an exothermic enthalpy diagram?
Downwards
Define endothermic
Heat is taken in from the surroundings (reactants gain energy)
What would happen to the temperature of the surroundings in an endothermic reaction?
It would fall
Which direction does Delta H go on an endothermic enthalpy diagram?
It goes upwards
Define standard enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from it’s constituent elements(all reactants and products in their standard states and under standard conditions)
Define standard enthalpy change of combustion
The enthalpy change that takes place when one mole of a compound reacts completely with oxygen(all reactants and products in their standard states and under standard conditions)
Define standard enthalpy change of reaction
The enthalpy change that accompanies a reaction in the molar quantities expressed in the chemical equation(all reactants and products in their standard states and under standard conditions)
Define standard conditions
1 atmosphere, 25*C, 1mol dm-3 for all solutions
Write an equation for the enthalpy change of combustion of Propane (C3H8)
C3H8(g) + 5O2(g) > 3CO2(g) + 4H2O(l)
Write an equation for the enthalpy change of combustion of CH3OH
CH3OH(l) + 1.5O2(g) > CO2(g) +2H2O(l)
Write an equation for the enthalpy change of formation of Sodium Carbonate (Na2CO3)
2Na(s) + C(s) + 1.5O2(g) > Na2CO3(s)
What is the equation do find the enthalpy change of reaction using DHF?
Products - reactants
Define Average bond enthalpy
The average enthalpy change that take place when breaking, by Homolytic bond fission, one mole of a give bond type in the molecules of a gaseous species
How do you calculate average bond enthalpy?
Add all the reactants enthalpy together, then add all the products enthalpy together but with a MINUS sign infront. Then add the two values together
What is the formula for heat energy lost/gained (Q)
Q=mcDeltaT
How do you calculate delta H?
Q(in kJ) / moles of reactant
How do you calculate the enthalpy of formation using DHC
Reactants - products
What sign shows exothermic
Negative
What sign shows endothermic
Positive
Why is the experiment value different to the data book value?
Because heat can get lost in the surroundings
Why is the value for the average enthalpy different from the real value?
Because it is only an average value
