Topic 8-Thermodynamics/Energetics I Flashcards
What is an exothermic reaction explain in energy and bonds?
Energy is being released to the surroundings and this means bonds are being formed
An example of exo is combustion
What is endothermic reactions in energy and bonds?
Endothermic reactions are when energy is taken in and this means bonds are being broken
Photosynthesis is an example
What is the first law of thermodynamics?
Energy can neither be created or destroyed but transferred from one to another
What is activation energy?
Minimum amount of energy required for a reaction to occur
What is the formula for Total energy for reactants?
Total EOR=Total EOP + energy lost or gained
What is enthalpy?
Measure of heat content of a substance at a constant temperature and pressure
KJ/mol
Explain the relationship between stoichiometry and enthalpy?
Enthalpy is directly proportinal to stochiometry
If all moles of substance are doubled than Enthalpy is doubled
Define standard enthalpy of formation?
Enthalpy Change when One mole of a substance is formed in its standard state from its elements in their standard states
What is standard enthalpy of combustion?
When one mole of a substance undergoes complete combustion under standard conditions
Where all reactants and products are in their standard states
What is calorimetry?
Involves the practical determination of enthalpy changes usually involves heating or cooling known amounts of water
Equation for heat energy?
Energy=mass×SHC×change in temp
Explain some inaccuracies due to calorimetry?
Heat lost to surroundings-not all heat is transferred to fuel
Incomplete combustion-fuel may not burn properly
Evaporation of fuel-some fuels evaporates instead of combusting
Heat absorbed by calorimeter
Explain the process of Measuring the Change in Temperature?
Temp is taken every 30s for 3 min to ensure the change in temp is constant
Reactants are mixed after 3 mins
Let reaction complete
Further readings taken every 30s as reaction cools,so change in temp is decreasing
We extrapolate to calculate value of change in temp
Why do we extrapolate the graph when measuring change in temperature?
We extrapolate as energy is being lost due to ongoing reaction,so by extrapolating the graph so its perpendicular to constant temp,we mitigate this and make it more accurate
Define standard enthalpy of neutralisation?
Enthalpy change when an acid and alkali react together under standard conditions to form 1 mol of water
Define standard enthalpy change of reaction?
Enthalpy change when a reaction occurs in molar quantities shown chemical equations
How to find enthalpy changes of combustion and why is a calorimeter required?
It’s harder to measure the temperature change of a reaction when one the reactants is a gas
A calorimeter helps with finding the temperature change
Use equation q=mct
Explain what Hess’s law is?
The total enthalpy change is independent of the route taken
The total enthalpy change is always the same no matter of the route taken
Explain the titration procedure in calculating the standard enthalpy change of neutralisation?
Pipette 25cm³ of acid into a polysterene cup and measure the temperature
Add 1 mol/dm³ of NAOH from a burette in 2cm³ portions,starring and measuring the temperature each time
Ads 8cm³ of acid after max temp has been reached
Plot a graph of volume of acid with temperature
Extrapolate the graph and find the intersection
What is bond enthalpy?
Amount of energy required to break 1 mol of a bond type in a molecule in gaseous state
