Chapter 9 Enthalpy changes Flashcards
Law of conservation of energy?
Energy cannot be created or destroyed, only transferred
Enthalpy?
Measure of heat energy present in a system
What letter represents enthalpy
H
Enthalpy change?
Energy released or taken in during a chemical reaction
Exothermic reaction?
Reaction which releases energy to the surroundings
Is the enthalpy change value for an exothermic reaction pos or neg
Neg
Endothermic reaction?
Reaction which takes in energy from the surroundings
Is the enthalpy change value of an endothermic reaction pos or neg
Positive
Activation energy?
Minimum energy requires for a reaction to take place
Symbol for activation energy
E subscript a
Why are standard conditions relevant to enthalpy changes
The enthalpy change of a reaction can vary depending on the conditions provided
What are the standard condition? 4
100kPa (approx 1atm pressure)
298 K (25°c)
1 mol dm^-3 (relevant for sols)
Standard state
what is standard state
The state of a substance under standard conditions e.g H2O is liquid
Is RTP the same as standard conditions
No
Symbol for standard conditions
circle with a line through
Definition for standard enthalpy change of reaction? 3 parts
The enthalpy change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions
units for enthalpy change
kJ mol^-1
Definition for standard enthalpy change of formation 2parts
The enthalpy change associated with the formation of one mole of a compound from its elements under standard conditions
What is the enthalpy change of formation for an element
Zero
Definition for standard enthalpy change of combustion
The enthalpy change associated with the complete combustion of one mole of a substance under standard conditions
Definition for standard enthalpy change of neutralisation 3 parts
The enthalpy change associated with the formation of one mole of water from a naturalisation reaction between an acid and a base, under standard conditions
What iss the value of the enthalpy change of neutralisation for the reaction between a strong acid and base
-57 km mol^-1
Is standard enthalpy change of combustion always pos or neg, why?
Always neg bc combustion is an exothermic reaction
Why is standard enthalpy change of neutralisation normaly the same value across different reactions?
Bc the same half equation is maintained: one mol of H+, one mol of OH- to form one mol oh H2O
Subscript of standard enthalpy change of neutralisation
neut
subscript of standard enthalpy change of combustion
c
subscript of standard enthalpy change of formation
f
subscript of standard enthalpy change of reaction
r
symbol for heat energy (Not enthalpy)
q
equation for calculating heat energy transferred between a system and its surroundings
q=mc delta T
unit for specific heat capacity (c)
J g^-1 K^-1
Unit for temp
Kelvin
how can we more accurately calculate change in temp experimentally
with a cooling curve extrapolation
Hiw do you produce a cooling curve extrapolation
Take temp of sol at short, regular intervals
Add other reactant to sol
Record temp of reaction mixture at regular intervals
Plot a cooling curve
Extrapolate the line of best fit and draw a line up from the x axis front he time the reactants were added to the sol
The crossing point of the 2 lines is the max temp
what is the function of a cooling curve extrapolation
corrects for heat loss during the experiment
