Topic 8-Thermodynamics/Energetics I

Question 1

What is an exothermic reaction explain in energy and bonds?

Answer 1

Energy is being released to the surroundings and this means bonds are being formed
An example of exo is combustion

Question 2

What is endothermic reactions in energy and bonds?

Answer 2

Endothermic reactions are when energy is taken in and this means bonds are being broken
Photosynthesis is an example

Question 3

What is the first law of thermodynamics?

Answer 3

Energy can neither be created or destroyed but transferred from one to another

Question 4

What is activation energy?

Answer 4

Minimum amount of energy required for a reaction to occur

Question 5

What is the formula for Total energy for reactants?

Answer 5

Total EOR=Total EOP + energy lost or gained

Question 6

What is enthalpy?

Answer 6

Measure of heat content of a substance at a constant temperature and pressure
KJ/mol

Question 7

Explain the relationship between stoichiometry and enthalpy?

Answer 7

Enthalpy is directly proportinal to stochiometry
If all moles of substance are doubled than Enthalpy is doubled

Question 8

Define standard enthalpy of formation?

Answer 8

Enthalpy Change when One mole of a substance is formed in its standard state from its elements in their standard states

Question 9

What is standard enthalpy of combustion?

Answer 9

When one mole of a substance undergoes complete combustion under standard conditions
Where all reactants and products are in their standard states

Question 10

What is calorimetry?

Answer 10

Involves the practical determination of enthalpy changes usually involves heating or cooling known amounts of water

Question 11

Equation for heat energy?

Answer 11

Energy=mass×SHC×change in temp

Question 12

Explain some inaccuracies due to calorimetry?

Answer 12

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

Question 13

Explain the process of Measuring the Change in Temperature?

Answer 13

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

Question 14

Why do we extrapolate the graph when measuring change in temperature?

Answer 14

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

Question 15

Define standard enthalpy of neutralisation?

Answer 15

Enthalpy change when an acid and alkali react together under standard conditions to form 1 mol of water

Question 16

Define standard enthalpy change of reaction?

Answer 16

Enthalpy change when a reaction occurs in molar quantities shown chemical equations

Question 17

How to find enthalpy changes of combustion and why is a calorimeter required?

Answer 17

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

Question 18

Explain what Hess’s law is?

Answer 18

The total enthalpy change is independent of the route taken
The total enthalpy change is always the same no matter of the route taken