Exam 3 Flashcards
When do you use “Products - Reactants”?
Any of these three cases:
When you have a table of delta H standard formation values.
When you have a table of delta G standard formation values.
When you have a table of standard S values.
Enthalpy has what symbol?
H
Entropy has what symbol?
S
Gibbs energy has what symbol?
G
What variable relates to heat?
It is actually q (lower case!), but for this class that’s the same as delta H.
What variable relates to randomness?
S
What must be true if given the current conditions a reaction will shift to form products?
Q < K and delta G < 0
What must be true if given the current conditions, a reaction will shift to form reactants?
Q > K and delta G > 0
What must be true when a reaction is at equilibrium?
Q = K and delta G = 0
What must be true if a reaction generally favors products?
K > 1 and delta G standard < 0
What must be true if a reaction generally favors reactants
K < 1 and delta G standard > 0
When should you use “Reactants - Products”
When you are given a table of bond enthalpies. It’s the problems where you need to draw Lewis structures.
What is the freezing point and boiling point of water?
Freezing: 0 degrees Celsius. Boiling 100 degrees Celsius
You are doing a calorimetry problem where one object is changing its temperature. What equation do you start with?
Delta H = m C (Tf - Ti)
You are doing a calorimetry problem where two substances are changing their temperature. What equation do you start with?
m C (Tf - Ti) + m C (Tf - Ti) = 0
How do you find out which chemical is the limiting reagent?
Convert everything to moles and then use the mole to mole ratio in the balanced reaction to figure out which reactant makes fewer moles of product.
You are doing a calorimetry problem where a chemical reaction is performed in water. What equation(s) do you use?
Delta H process + m C (Tf - Ti) = 0
and also use “the ratio”
You are doing a calorimetry problem where a chemical reaction is performed in a calorimeter and that calorimeter is put in water. What equation(s) do you use?
Ccal (Tf - Ti) + Delta H process + m C (Tf - Ti) = 0
and also use “the ratio”
When it comes to units, what two common mistakes should you be on the lookout for in your work?
Make sure you don’t use kJ and J in a single equation.
Make sure all temperatures are in Kelvin (temperature CHANGES can stay in Celsius)
When do you use “Products OVER Reactants”
When you are calculating Q or you are calculating K from current pressures or molarities.
(Don’t forget your exponents, and watch out for solids and liquids)
For an entropy dominated reaction, raising the temperature will shift the reaction to which side?
It will shift towards the more random side
The side with more gas. Or if there is no gas at all, then the side with more liquid/aqueous)
When you flip a reaction, what do you do to its delta H value?
Flip the sign. This also what you do for its delta S value and its delta G value.
When you multiply a reaction by a constant, what do you do to its delta H value?
You multiply the delta H by that constant. This also what you do for its delta S value and its delta G value.
When you sum up reactions, what do you do with their delta H values.
You also sum up their delta H values. This also what you do for its delta S value and its delta G value.
