Chemistry Study Guide #6
Energy is the
capacity to do work.
Chemical reactions are considered favorable if the
products have a lower energy than the reactants.
The energy of the reacting molecules affects
whether a particular collision will lead to a chemical reaction.
The rusting of iron is described by the reaction: 4 Fe(s) + 3 O2(g) 2 Fe2O3(s).
-The formation of rust on an exposed piece of iron typically takes several months. -The formation of rust has a low reaction rate. -The formation of rust has a high activation energy. -The formation of rust would occur more slowly at higher altitudes where the concentration of oxygen is lower. -The formation of rust would occur faster in the warmer summer months than in the cooler winter months.
The activation energy for the reaction is ______
1
calorie=
1 calorie
Calorie =
1000 calories
Which of the following energy quantities is equivalent to 258 Cal?
1Kcal =4.184Kj ??
Which of the following energy quantities is equivalent to 878 J?
1Kcal =4.184Kj ??
A chemical reaction releases 1055.2 kcal. How many kilojoules does this correspond to?
1Kcal =4.184Kj approx: 4,414.95→4,415
Which Kj energy quantities is equivalent to 14.9 kcal?
1Kcal =4.184Kj approx: 62.34→62 kcal
A chemical reaction requires 62.29 kJ. How many kilocalories does this correspond to?
1Kcal =4.184Kj approx: 14.8→15 kcal
Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where H = 130 kJ. How many kilojoules are released when 2.5 mol of C2H4 reacts? 2.5mol x 130Kj = ____________
325 Kj
Consider the reaction: M3(g) + Kl2(g) MKl5(g). If [M3] = 0.39 M, [Kl2] = 0.22 M, and [MK5] = 0.44 at equilibrium, what is the value of K? K= Products Reactants K= [ MK]5 =_________ [ M]3 [Kl]2
???
Which statement concerning the reversible reaction 2 NO2(g) N2O4(g) is true?
As the forward reaction progresses and more N2O4 is formed, the reverse reaction rate increases.
Energy diagram labels
B = ∆H C = Transition state D = products E = reactants
Which quantity represents the largest amount of stored energy: fat, carbohydrate or protein?
Energy is stored in the body as fat Fat=9cal/gm, Protein and cholesterol RE 4cal/gm
A peanut butter and jelly sandwich contains 12.00 g of fat, 8.00 g of protein, and 25.0 g of carbohydrate. How many Calories does this sandwich provide?
Fat=9cal/gm, Protein and cholesterol = 4cal/gm =240 calories
What will increase the rate of a reaction?
Increasing the temperature, increasing the concentration of a reactant, adding a catalyst, ensuring that the reactants are properly aligned when they collide.
What is the expression for the equilibrium constant for the reaction: 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g)?
K= Products ------------------------ Reactants [ CO2] 4 [H2O]5 ------------------------- [ C2H6]2 [O2]
What is the gas phase chemical reaction that corresponds to the equilibrium constant expression shown below?
K= [ C] 2 --------------- [ A]4 [B]2 4 A + 2 B *double→ 2 C
Consider the reversible reaction: M(g) + Kl2(g) MKl2(g). The reverse reaction is
MKl2(g) → M(g) + Kl2(g).
Consider the reaction: C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O(g), where H = -531 kcal. Which statement concerning this reaction is true?
The bonds formed in the products are stronger than the bonds broken in the reactants because the heat change is negative.
Consider the reversible reaction at equilibrium: M2(g) + K2(g) 2 MK(g). What is the effect of removing some M2(g) from the equilibrium system?
The concentration of K2(g) increases.
When the pressure of a reaction at equilibrium decreases, in which direction does the equilibrium shift?
The equilibrium shifts in the direction that increases the number of moles of gas.
Which bond is the weakest? H-H=+104 Cl-Cl=+58
The less pos the weaker, thus the Cl-Cl bond is weaker.
Which bond is the strongest? H-H=+104 Cl-Cl=+58
The more pos the stronger, thus the H-H bond is stronger.
Which of the following is NOT a reasonable assumption about the chemical reaction whose energy diagram is depicted below?
The rate of a chemical reaction increases with an increase in the concentration of one or more reactants, as the higher concentration of reactants increases the frequency of collisions between molecules.
When reactants can come together and form products, and products can come together to re-form reactants, the reaction is called
a reversible reaction.
Enzymes are proteins that
act as biological catalysts.
Bond dissociation energies are
always positive numbers.
Heat is absorbed in
an endothermic reaction.
Potential energy is the energy inherent in
an object due to its position or composition.
An equilibrium constant with a value of 4.0 x 106 indicates that
at equilibrium the products are favored (because the value is greater than 1)
An equilibrium constant with a value of 4.0 x 10-6 indicates that
at equilibrium the reactants are favored (because the value is less than 1) .
The stronger the bond, the higher its
bond dissociation energy.
Walking at a brisk pace burns off about 110 Cal/mile. How far would you have to walk to burn off the Calories obtained from eating a candy bar that contained 4 g of protein, 16 g of fat, and 9 g of carbohydrates?
candy bar= 196 calories Almost two miles.
Changes in potential energy occur in
chemical reactions.
It is always necessary for a chemical reaction to occur between two reactants (A and B). A and B must
collide with the proper orientation and with a certain minimum amount of energy.
Ammonia (NH3) is synthesized by the reaction of nitrogen and hydrogen in the presence of an iron catalyst according to the equation below. Removing the iron catalyst would
decrease the reaction rate.
Consider the reaction: 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g). Decreasing the concentration of C2H6(g) will
decrease the reaction rate.
As a general rule, a reaction rate doubles for
each 10 degrees Celsius the temperature is raised.
Bond breaking is
endothermic.
An endothermic reaction is one in which
energy is absorbed and ∆H is pos (+).
Breaking a chemical bond requires
energy.
A reversible reaction has reached equilibrium when the condition is
established of the forward and reverse reaction rates become equal.
Le Châtelier's principle is a general rule used to
explain the effect of a change in reaction conditions on equilibrium.
Reactions with high Ea are
generally slow reactions.
In the reaction: C2H6(g) + O2(g) → CO2(g) + H2O(g), increasing the concentration of C2H6(g) (the reactants) will
increase the reaction rate.
Increasing the temperature of a reaction mixture usually results in
increased decrease in the reaction rate.
When the equilibrium constant for a reversible reaction is much greater than one (K > 1), the equilibrium is said to
lie to the right.
In an exothermic reaction, the products are
lower in energy than the reactants.
Catalysts accelerate a reaction by
lowering the energy of activation.
Activation energy is the
minimum amount of energy necessary for a reaction to occur.
When heat is added to an exothermic equilibrium reaction, the reaction shifts to form
more reactants.
Kinetic energy is the energy associated with
movement.
A catalytic converter uses a catalyst to catalyze three reactions that clean up the exhaust from an auto engine. The elements used as a catalyst in catalytic converters are
platinum, rhodium, and palladium.
Exothermic reactions involve the formation of
products having lower energy than the reactants.
For an endothermic reaction at equilibrium, increasing the temperature increases the
rate of the forward reaction to form more products.
Once equilibrium is reached in a chemical reaction,
reactants may continue forming products.
When ∆H is negative, the bonds formed in the products are
stronger than the bonds broken in the reactants.
The hydrolysis of sucrose depicted below has K = 1.4 x105. Which of the following is a reasonable assumption about this reaction once equilibrium is established?
sucrose + H2O glucose + fructose The equilibrium mixture contains mostly glucose and fructose.
The law of conservation of energy states
that energy cannot be created or destroyed.
W catalysts catalyst increases the rate of a chemical reaction, A catalyst lowers
the activation energy of a chemical reaction and A catalyst is recovered unchanged in the reaction it catalyzes.
The difference in energy between the reactants and the transition state is called
the energy of activation, symbolized by Ea.
Endothermic describes a reaction in which
the energy of the products is higher than the energy of the reactants.
Increasing the concentration of the reactants in a chemical reaction increases
the number of collisions, and the reaction rate increases.
