Unit 6 Flashcards
Thermochemistry
-∆H? Endothermic or exothermic
Exothermic
∆H? Endothermic or exothermic
Endothermic
Formula for ∆H?
Hproducts-Hreactants
Does Endothermic absorb or give off
Absorb
Does exothermic absorb or give off
Give off
∆E formula
∆E= q (heat)+w (work)
Positive w value?
Work is being done on the system
Negative w value
Work is being done by the system
For endothermic reactions, are the products higher than the reactants?
Yes
Fusion, Endo or exo?
Endothermic
Freezing, Endo or exo?
Exothermic
Condensation, Endo or exo?
Exothermic
Vaporization, Endo or exo
Endothermic
Sublimation, Endo or exo?
Endothermic
Deposition, Endo or exo?
Exothermic
Does endothermic involve breaking bonds or making bonds?
Breaking
Does exothermic involve breaking or making bonds?
Making
Can dissolving be endothermic, exothermic, or both
Both
Dissolution formula
∆H1+∆H2+∆H3=∆H solution
The bottom of a beaker is frozen to a wooden board (the beaker has a reaction taking place in it)
Is that exothermic or endothermic?
Is it a physical change or a chemical change?
An endothermic chemical change because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction
(Surroundings = board & beaker, got colder due to reaction taking place IN the beaker)
Cl(g) + e- = Cl- (g)
Endothermic or exo
thermic?
Exothermic. Gaining an electron to become more stable lowers the overall energy
If you use a catalyst to lower the activation energy (Ea), what does it do to the enthalpy (∆H)?
Nothing. The catalyst isn’t consumed in the reaction so it doesn’t matter. The path it takes doesn’t matter, just the energy of the reactants & products
What is activation energy used for?
Breaking bonds/intermolecular forces
Also used to initiate a reaction
Difference between enthalpy change and activation energy?
Enthalpy change— measures the difference in the initial and final states (The net energy released or added). Depends solely on the chemical composition of the reactants and products
Activation energy— energy required to start a reaction. Depends on path taken
What is temperature?
A measure of the average kinetic energy of the particles of the sample
What is average speed? (Formula)
The total distance traveled/ the total time taken
What are the units for c (specific heat)?
Jkg•K or J/g•k (°C can be used in place of Kelvin)
What are the units for C (heat capacity)
J/K or J/°C
What is the specific heat of water?
4.184 J/(g•°C)
Why would 1g of a metal have the same change in temperature vs 4g of water?
Water has a higher specific heat capacity
Hess’s law:
Calculate the standard enthalpy change (∆H) for the combustion of methane:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
given the following reactions and their standard enthalpy changes:
C(s) + O₂(g) → CO₂(g) ΔH° = -393.5 kJ
H₂(g) + ½O₂(g) → H₂O(l) ΔH° = -285.8 kJ
C(s) + 2H₂(g) → CH₄(g) ΔH° = -74.8 kJ
- Leave the first, double the second, flip the last. Do the same with the numbers
- -890.3 kJ
