Energetics Flashcards
(14 cards)
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.
