Module 13 Flashcards
In a chemical reaction, where is the potential energy? Where is the kinetic energy?
The potential energy is in the bonds of the molecules in the reaction. Kinetic energy is the heat that is either absorbed or released in the reaction.
If a chemical reaction has a positive AH, will the beaker that contains the reaction feel hot or cold once the reaction is finished?
Cold
Why is Hess’s law a more exact way of determining AH than the technique that uses bond energies?
It is more exact because it also takes into account the phases of each substance in the reaction.
What is a state function? Give 2 examples
It is a function whose final value is independent of it’s path. Enthalpy and Gibbs free energy
Which of the following substances will have a AHf* of 0?
NaOH (aq) Na+ (aq) O2 (g) O (g) Cl2 (g) H2 (l)
O2 (g) Cl2 (g)
1) What is a defining property of an endothermic graph?
2) What is a defining property of an exothermic graph?
3) How do you figure out the AH of a reaction from a graph?
4) What do you draw to signify a large activation energy?
5) What do you draw to signify a low activation energy?
1) For an endothermic graph the second half of the graph (the product) is higher than the first half (the reactant)
2) For an exothermic graph the second half of the graph is lower than the first half.
3) You minus the number value of the reactant line from the number value of the product line (# P - # R).
4) A large hump,
5) A small hump
If you have 2 50.0 kg blocks of copper, and one is at a temperature of 50C while the other is at a temperature of 25C, which has more entropy?
The warmer block has the higher entropy
If a chemical reaction is exothermic but has a negative AS, what could you do to the temperature to make it possible to run the reaction?
Lower the temperature to make the TAS smaller.
Hess’s Law:
Enthalpy is a state function
The Enthalpy of formation is
(🔺Hf) The 🔺H of a formation reaction.
The equation of Hess’s Law:
🔺H* = (sum of) 🔺Hf* (products) - (sum of) 🔺Hf* (reactants)
What is significant of the standard enthalpy of formation of an element.
The standard enthalpy of formation of an element in its ELEMENTAL FORM is 0.
What is energy considered in an exothermic reaction?
What is energy considered in an endothermic reaction?
exo - energy is considered a product
endo - energy is considered a reactant
What is the Change in Enthalpy
(AH) The energy change that accompanies a chemical reaction
What is the AH sign for exothermic and endothermic reactions? What happens to the Heat?
endo = + Heat is absorbed exo = - Heat is released
What is Standard conditions?
It is the temperature and pressure that most chemical reactions or done in. Room temperature (25*C) and Normal atmospheres (1.00 atm)
What is an energy diagram? And what does it convey? What is its X and Y names?
It is a picture of a chemical reaction. The AH and the activation energy. (the intermediate state is at the top of the hump aka activation energy) x- reaction coordinate y- Energy (kJ)
What is activation energy?
It is the energy necessary to start a chemical reaction.
What is Entropy?
It is a measure of the disorder that exists in any system
The Second Law of Thermodynamics:
The entropy of the universe must always either increase or remain the same. It can never decrease.
(AS universe >= 0)
Entropy and phases. Entropy and Temperature. Entropy and matter.
It increases from solids to gases. It increases with increasing temperature. Entropy increases with increasing matter.
What has absolute entropy?
All substances even elements
Gibbs free energy equation is
AG = AH - T x AS
When is a reaction spontaneous. What does this mean?
When AG < 0. It is consistent with the second law
1) When there is more entropy on the reactant side the sign is
2) When AH is negative it goes on the _______ side
3) When there is more entropy on the product side the sign is
4) When the AH is positive it goes on the ______ side
1) Negative
2) Product
3) Positive PRODUCT POSITIVE
4) Reactant
How do you find the activation energy?
The intermediate point - the reactants
AH stands for:
a. The potential energy associated with a substance
b. the enthalpy of a molecule
c. The potential energy change associated with a reaction
d. None of the above
C. the potential energy change associated with a reaction.
