Endothermic and Exothermic Processes
Energy Diagrams and Heat Transfer
Calorimetry and Phase Changes
Enthalpy of Reaction and Formation
Hess’s Law
100
What is the difference between an endothermic and exothermic reaction?
An endothermic reaction absorbs heat, while an exothermic reaction releases heat.
100
In an exothermic reaction, are products higher or lower in energy than reactants?
Lower
100
What is the formula used to calculate heat transfer?
q=mcΔT
100
What symbol represents enthalpy change?
ΔH
100
What does Hess’s Law state?
The total ΔH is the sum of ΔH values for each step
200
What happens to the temperature of the surroundings during an exothermic reaction?
It increases
200
Which letter represents the activation energy?
C
200
Is condensation exothermic or endothermic and why?
Condensation is exothermic because it releases heat as gas particles lose energy and form liquid.
200
Is a reaction with negative ΔH endothermic or exothermic?
Exothermic
200
What happens to ΔH when a reaction is reversed?
It's sign is switched (Ex: positive to negative)
300
Is freezing water endothermic or exothermic?
Exothermic
300
What is thermal equilibrium?
When two objects reach the same temperature and no heat flows
300
What are the 4 different ways to find heat?
1) q=mcΔT
2) bond enthalpies of bonds broken - bond enthalpies of bonds formed
3) standard enthalpy of products - standard enthalpy of reactants
4) Hess's Law
300
What is standard enthalpy of formation?
ΔH when 1 mole of a compound forms from elements in standard states
300
How do you find overall ΔH when adding reactions?
Add the ΔH values
400
Is boiling water endothermic or exothermic, and why?
Endothermic; energy is needed to break intermolecular forces
400
How does a catalyst change an energy diagram?
It lowers the activation energy
400
How much heat is absorbed by 100 g of water heated from 25°C to 75°C? (c = 4.18 J/g·°C)
20,900 J
400
How do you calculate ΔH of bonds formed/broken?
ΔH (formed)=number of bonds formed×(bond enthalpy)
400
What must you do if you multiply a reaction by a coefficient?
Multiply ΔH by the same number
500
A beaker feels cold during a reaction. What type of process is this, and why?
Endothermic; heat is absorbed from the surroundings
500
Which is the rate determining step and how would you identify this on a PES graph?
The slow step is the rate determining step and it is the one with the highest activation energy.
500
Why doesn’t temperature change during a phase change?
Heat is used to break intermolecular forces
500
Write the formation reaction for CO₂(g).
C(s) + O₂(g) → CO₂(g)
500
Use Hess’s Law:
C(s) + O₂(g) → CO₂(g); ΔH = -393.5 kJ
CO(g) + ½O₂(g) → CO₂(g); ΔH = -283.0 kJ
Find ΔH for: C(s) + ½O₂(g) → CO(g)
+110.5 kJ