Energetics Flashcards
What are ‘Standard Conditions’ (ᶱ).
298Kelvin and 100kPascals
What is, Enthalpy change (ΔH).
The amount of heat energy taken in or given out during any change in a system, provided the system is kept at constant pressure.
What does an Exothermic reaction look on a graph?
Enthalpy ΔH
│Reactants
│—————————-
│ │
│ │ - ΔH
│ │
│ │
│ │
│ ↓ Products
│ —————————-
│
The products have less energy and ΔH is –ve
What does an Endothermic reaction look on a graph?
Enthalpy ΔH
│ Products
│ —————————-
│ ↑
│ │ + ΔH
│ │
│ │
│ │
│ Reactants │
│—————————-
│
The products have more energy and ΔH is +ve
What is Calorimetry?
Calormitery is the process of measuring enthalpy change of a reaction, this is done by measuring temperature change (ΔT) and using specific heat capacity (c).
What is the calculation to find heat transferred?
q=mcΔT
In q=mcΔT what does each letter stand for?
q = heat energy transferred (KJ)
m = mass (g)
c = specific heat capacity (J.g-1.K-1)
ΔT = change in temperature (K)
What does a heat energy transferred graph look like?
Temperature
│
│
│ ↑ x x
│ | x x (IMAGINE LINE OF BEST FIT)
│ | x
│ | x x
│ | x
│ |
│ ΔT |
│ |
│ |
│ |
│ |
│ |
│ |
│ |
│-x-x-x-x—————–
│
│
___________________________________
Time in Minutes
What is the formula for % of error?
% Error =
(Experimental Value - Accepted Value)
_____________________________ x 100
Accepted Value
What is Standard Enthalpy of Combustion ΔHcᶱ?
The enthalpy change when 1 mole of a substance burns completely in oxygen under standard conditions.
What is the formula for the complete combustion of an alkane?
(CnH2n+2) + (2n+2 O2) –> (n CO2) + (2n+2 H2O)
What does the term ‘Constituent Elements’ mean?
They are the elements making up a compound, for example if the compound in a question was H2SO4, the constituent elements would be:
H2(g) + S(s) + 2O2(g) -> H2SO4(aq)
What is Standard Enthalpy of Formation ΔHfᶱ?
The enthalpy change when 1 mole of a substance forms from it’s constituent elements under standard conditions.
What is Hess’s Law?
The enthalpy change for a reaction depends only on the initial and final states of the reaction and is independent of the route by which the reaction may occur.
