Chl. 6/ Energy Rates And Equimirbirum Flashcards
What is energy?
The capacity to do work.
What is potential energy?
Potential energy is stored energy.
What is kinetic energy?
Kinetic energy is the energy from motion.
What is the Law of conservation of energy?
It statuses that the total energy in a system does not change.
(Energy cannot be created or destroyed)
What do chemical bonds do?
Chemical bonds store potential energy.
Reactions that form products having……… than the reactants are favored?
Lower potential energy.
What does 1 calorie equate to in joules ?
1 cal= 4.184 J
What are the larger units of calories and joules?
Kilojoules (KJ) and Kilocalories (kcal)
1,000 J = ? kJ?
1,000 J = 1 KJ
1,000 cal = ? kcal
1,000 cal = 1 kcal
1 kcal = ? kJ
1 Kcal = 4.184 kJ
When calories come together and react, bonds are 1. (broken/formed in the reactants and new bonds are 2. (broken/ formed) in the products.
- Broken
- Formed
- What does bond breaking always require?
- What does bond formation always release?
- Input of energy
- Release energy
What does it mean to cleave a bond?
To cleave a bond means to separate or break it apart.
What does ΔH stand for?
ΔH is the energy absorbed or released in a reaction. Its is called the heat of reaction or the enthalpy change.
What does the Heat of Reaction mean?
- The heat of reaction, represented by ΔH, specifically refers to the heat energy released or absorbed during a chemical reaction at constant pressure.
- It indicates the amount of heat transferred between the system (the chemical reaction) and its surroundings.
What is Enthalpy change?
- Enthalpy change, also represented by ΔH, encompasses not only the heat of reaction but also any changes in the internal energy of the system and the work done on or by the system. It includes changes in heat content and the expansion or compression work done during the reaction.
In summary, while the heat of reaction is a specific subset of the enthalpy change, enthalpy change includes all energy changes that occur during a reaction, making it a broader concept.
What is an Endothermic reaction?
When energy is absorbed, the reaction is said to be endothermic and ΔH is positive (+)
What is an exothermic reaction?
When energy is released, the reaction is said to be exothermic and ΔH is negative (-).
What is bond dissociation energy ?
(Bind energy)
The bond dissociation energy is ΔH for breaking a covalent bond by equally dividing the e- between the two atoms.
Are bond dissociation energies, positive positive or negative values?
Bond dissociation energies are positive values, because bond breaking is endothermic. (ΔH>0)
True or False?
Bond formation always has negative values, because bond formation is exothermic. (ΔH<0)
True
True or False?
The stronger, the bond, the higher, its bond, dissociation energy.
True
How do bond dissociation energies decrease on the periodic table?
In comparing bonds formed from elements in the same group, bond, dissociation energies, generally decreased going DOWN the COLUMN.
What does ΔH indicate in terms of bonds?
ΔH indicates the relative strength of the bonds, broken and formed in a reaction.
When is ΔH negative? 📍
(2 explanations)
• ΔH is negative when more energy is released informing bonds, then is needed to break the bonds .
• ΔH is negative when the bond formed in the products are stronger than the bonds broken in the reactants.
When is ΔH positive? 📍
(2 explanations)
• ΔH is positive when more energy is needed to break bonds, then is released in the formation of new bonds.
• ΔH is positive when the bonds broken in the reactants are stronger than the bonds formed in the products.
How can you identify an endothermic reaction? 📍
• heat is absorbed
• ΔH is positive
• the bonds broken in the reactants are stronger than the bonds formed in the products
• the products are higher in energy than the reactants
How can you identify an exothermic reaction ?📍
• heat is released
• ΔH is negative
• the bonds formed in the products are stronger than the bonds broken in the reactants
• the products are lower energy than the reactants
Calorimetry 📍
ΔH = q = m • c • ΔT
What do the abbreviations stand for?
q= heat lost or gained
m= mass in grams
c= specific heat capacity
ΔT= T final - T initial
Note: the specific heat capacity (c) of a substance is the quantity of heat required to change the temperature of 1 gram of the substance by 1 K.
What does the Specific Heat stand for?
• the specific heat is the amount of heat energy (cal or J) needed to raise the temperature of 1 g substance by 1°C.
What is the Specific heat equation?
Specific heat= heat/ mass • ΔT = cal (or J)/ g • ΔT
True or False?
The larger the specific heat, the less its temperature will change when it absorbs a particular about of heat energy .
True
For Chapter 6 learn how to calculate the heat absorbed, given specific heat. (Slide 16)
Example: how many calories are needed to heat a pot of 1600 g of water from 25°C to 100.°C?
• Step 1: identify the known quantities and the desired quantity
Mass= 1600 g
T1= 25°C
T2= 100.°C
Known Quantities
? Calories
Desired quantities
ΔT= T2-T1= 100°C -25°C = 75°C
The specific heat of water it 1.00 cal/(g• °C)
• Step 2: Write the Equation
The specific heat is a conversion factor that relates the heat absorbed to the temperature change (ΔT) and mass.
Heat= mass • ΔT • specific heat
Cal= g • °C • (cal/g• °C)
• Step 3: solve the equation
- substitute the known quantities into the equation and solve for the heat in calories.
cal= 1600g • 75°C • (1.00 cal/ 1g • 1°C)
= 1.2 • 10^5 cal
To learn how to calculate the amount of heat from a temperature temperature change see SLIDE 19 Chapter 6.
For a reaction to occur, what must happen?
For a reaction to occur, two molecules must collide with enough kinetic energy to break bonds. The orientation of the two molecules must be correct as well.
See slide 22 for image
What is the energy activation? Slide 23
Ea, the energy of activation, is the difference in energy between the reactants and the transition state.
True or False?
- The Ea is the minimum amount of energy that the reactants must possess for a reaction to occur.
- Ea is called D energy barrier and the height of the barrier determines the reaction rate.
- When the Ea is high, few molecules have enough energy to cross the energy barrier, and the reaction is slow.
- When the Ea is low, many molecules have enough energy to cross the energy barrier, and the reaction is fast.
True
True
True
True
True or False?
The difference in energy between the reactants and the products is the ΔH.
True
If ΔH is negative, the reaction is…..?
Exothermic
If the ΔH is positive, the reactions is….?
Endothermic
What is a catalyst and what does it do?
• a catalyst is a substance that speeds up the rate of a reaction
• a catalyst is recovered, unchanged in a reaction and does not appear in the product
• catalysts accelerate a reaction by lowering Ea without affecting the ΔH
What is the difference between the catalyzed reaction and the un catalyzed reaction?
• The uncatalyzed reaction (higher Ea) is slower
• The catalyzed reaction (lower Ea) is faster
• ΔH is the same for both reactions.
Can reactions only go in one direction?
(Reversible reaction)
No.
• a reversible reaction is a reaction can occur in either direction
In which direction does a forward reaction move-in and in which direction does a reverse reaction move in?
• The forward reaction proceeds to the right
• The reverse reaction proceeds to the left
True or False?
1. The system is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction
- The net concentration of reactant and products do not change equilibrium.
- True
- True
What is the relationship between the concentration of the products and the concentration of the reactants known as?
The Equilibrium constant, K
What are brackets used for?
Slide 40
Brackets, [], are used to symbolize concentration in moles per liter
(Mol/L)
Study slide 41 to 48
If a chemical system at equilibrium is disturbed or stressed, the system will react in a direction that counteract the disturbance or relieves the stress.
What are some of the possible disturbances?
• concentration changes
• temperature changes
• pressure changes
See slides 51-57 to further understand/ learn how to sold Concentration changes in chemical equations.
Le Châtelier’s Principle
Le Châtelier’s Principle 📍
What effects does concentration have on equilibrium when….
- adding reactant
- removing reactant
- adding product
- removing product 
- Adding a reactant will affect the equilibrium to favor the products.
- Removing a reactant will affect the equilibrium to favor the reactants
- Adding a product will affect the equilibrium to favor the reactants.
- Removing a product will affect the equilibrium to favor the product.
Le Châtelier’s Principle 📍
In what ways does temperature affect equilibrium?
• By increasing the temperature in an endothermic reaction, equilibrium favors the products.
In an exothermic reaction, equilibrium favors the reactants.
• By decreasing the temperature in an endothermic reaction, equilibrium favors the reactants.
In an exothermic reaction, equilibrium favors the products.
Le Châtelier’s Principle 📍
What affects does increasing or decreasing the pressure on equilibrium?
• increasing the pressure
Equilibrium favors the side that has fewer moles
• decreasing the pressure
Equilibrium favors the side that has moles.
