Interpret Chemical Energy Diagrams - Chemistry
Card 1 of 30
Identify whether $\Delta H$ is positive or negative if $E_{TS}-E_R < E_{TS}-E_P$.
Identify whether $\Delta H$ is positive or negative if $E_{TS}-E_R < E_{TS}-E_P$.
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$\Delta H < 0$. If forward barrier is larger, products are lower than reactants.
$\Delta H < 0$. If forward barrier is larger, products are lower than reactants.
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Identify whether $\Delta H$ is positive or negative if $E_{a,reverse} < E_{a,forward}$.
Identify whether $\Delta H$ is positive or negative if $E_{a,reverse} < E_{a,forward}$.
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$\Delta H > 0$. If reverse barrier is smaller, products are higher than reactants.
$\Delta H > 0$. If reverse barrier is smaller, products are higher than reactants.
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What does a very small $E_a$ suggest about the reaction at room temperature?
What does a very small $E_a$ suggest about the reaction at room temperature?
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It can occur rapidly at room temperature. Low barriers allow reactions to proceed easily at moderate temperatures.
It can occur rapidly at room temperature. Low barriers allow reactions to proceed easily at moderate temperatures.
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In a 2-step diagram, step 1 has $E_a=30,\text{kJ}$ and step 2 has $E_a=65,\text{kJ}$. Which step is RDS?
In a 2-step diagram, step 1 has $E_a=30,\text{kJ}$ and step 2 has $E_a=65,\text{kJ}$. Which step is RDS?
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Step 2. The rate-determining step has the largest activation energy.
Step 2. The rate-determining step has the largest activation energy.
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What does it mean if the diagram shows products higher than reactants but a low peak?
What does it mean if the diagram shows products higher than reactants but a low peak?
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Thermodynamically unfavorable but can be kinetically fast. Thermodynamics opposes products, but kinetics allows rapid formation.
Thermodynamically unfavorable but can be kinetically fast. Thermodynamics opposes products, but kinetics allows rapid formation.
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What is the correct expression for $E_{a,reverse}$ using energies $E_{TS}$ and $E_P$?
What is the correct expression for $E_{a,reverse}$ using energies $E_{TS}$ and $E_P$?
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$E_{a,reverse} = E_{TS} - E_P$. Reverse activation energy uses product energy instead of reactant energy.
$E_{a,reverse} = E_{TS} - E_P$. Reverse activation energy uses product energy instead of reactant energy.
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Which quantity changes when temperature increases: $\Delta H$, reactant energy levels, or effective reaction rate?
Which quantity changes when temperature increases: $\Delta H$, reactant energy levels, or effective reaction rate?
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Effective reaction rate increases. Higher temperature provides more thermal energy to overcome barriers.
Effective reaction rate increases. Higher temperature provides more thermal energy to overcome barriers.
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What is true about product energy relative to reactant energy in an exothermic diagram?
What is true about product energy relative to reactant energy in an exothermic diagram?
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Products are at lower energy than reactants. Energy is released when products form, making them more stable than reactants.
Products are at lower energy than reactants. Energy is released when products form, making them more stable than reactants.
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What is true about product energy relative to reactant energy in an endothermic diagram?
What is true about product energy relative to reactant energy in an endothermic diagram?
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Products are at higher energy than reactants. Energy must be absorbed to form products, making them less stable than reactants.
Products are at higher energy than reactants. Energy must be absorbed to form products, making them less stable than reactants.
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What does a larger $E_a$ imply about reaction rate at the same temperature?
What does a larger $E_a$ imply about reaction rate at the same temperature?
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Slower reaction rate. Higher energy barriers require more thermal energy to overcome at given temperature.
Slower reaction rate. Higher energy barriers require more thermal energy to overcome at given temperature.
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What effect does a catalyst have on $E_a$ on an energy diagram?
What effect does a catalyst have on $E_a$ on an energy diagram?
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It lowers $E_a$. Catalysts provide alternative pathways with reduced energy barriers.
It lowers $E_a$. Catalysts provide alternative pathways with reduced energy barriers.
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What effect does a catalyst have on $H$ on an energy diagram?
What effect does a catalyst have on $H$ on an energy diagram?
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No change to $\Delta H$. Catalysts only affect the pathway, not the energy difference between states.
No change to $\Delta H$. Catalysts only affect the pathway, not the energy difference between states.
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What effect does a catalyst have on the energies of reactants and products?
What effect does a catalyst have on the energies of reactants and products?
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No change to reactant or product energies. Catalysts only lower the transition state energy, not endpoint energies.
No change to reactant or product energies. Catalysts only lower the transition state energy, not endpoint energies.
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What is the relationship between forward and reverse enthalpy changes?
What is the relationship between forward and reverse enthalpy changes?
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$\Delta H_{reverse} = -\Delta H_{forward}$. Forward and reverse reactions have equal but opposite energy changes.
$\Delta H_{reverse} = -\Delta H_{forward}$. Forward and reverse reactions have equal but opposite energy changes.
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Identify the quantity shown by the vertical gap from reactants to products on an energy diagram.
Identify the quantity shown by the vertical gap from reactants to products on an energy diagram.
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$\Delta H$. The overall energy change from reactants to products.
$\Delta H$. The overall energy change from reactants to products.
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Identify the quantity shown by the vertical gap from reactants to the peak on an energy diagram.
Identify the quantity shown by the vertical gap from reactants to the peak on an energy diagram.
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$E_a$ (forward). The energy barrier from reactants to the transition state.
$E_a$ (forward). The energy barrier from reactants to the transition state.
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Identify the quantity shown by the vertical gap from products to the peak on an energy diagram.
Identify the quantity shown by the vertical gap from products to the peak on an energy diagram.
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$E_a$ (reverse). The energy barrier from products back to the transition state.
$E_a$ (reverse). The energy barrier from products back to the transition state.
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Which feature on an energy diagram indicates a multistep reaction mechanism?
Which feature on an energy diagram indicates a multistep reaction mechanism?
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More than one peak (multiple transition states). Each peak represents a separate elementary step in the mechanism.
More than one peak (multiple transition states). Each peak represents a separate elementary step in the mechanism.
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What does each valley between peaks represent in a multistep energy diagram?
What does each valley between peaks represent in a multistep energy diagram?
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A reaction intermediate. Valleys represent unstable species formed between elementary steps.
A reaction intermediate. Valleys represent unstable species formed between elementary steps.
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In a multistep diagram, which step is the rate-determining step?
In a multistep diagram, which step is the rate-determining step?
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The step with the largest $E_a$ (tallest barrier). The slowest step has the highest activation energy barrier.
The step with the largest $E_a$ (tallest barrier). The slowest step has the highest activation energy barrier.
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What does a lower peak for a catalyzed pathway indicate compared with the uncatalyzed pathway?
What does a lower peak for a catalyzed pathway indicate compared with the uncatalyzed pathway?
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Lower activation energy for the catalyzed pathway. Catalysts reduce the energy barrier, increasing reaction rate.
Lower activation energy for the catalyzed pathway. Catalysts reduce the energy barrier, increasing reaction rate.
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What does it mean if the diagram shows two curves with the same start and end energies?
What does it mean if the diagram shows two curves with the same start and end energies?
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Same $\Delta H$, different $E_a$ (often catalyzed vs uncatalyzed). Same thermodynamic change but different kinetic pathways are shown.
Same $\Delta H$, different $E_a$ (often catalyzed vs uncatalyzed). Same thermodynamic change but different kinetic pathways are shown.
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What does the energy difference between reactants and products determine about equilibrium?
What does the energy difference between reactants and products determine about equilibrium?
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Thermodynamic favorability (relative stability), not rate. Energy difference determines equilibrium position, not how fast equilibrium is reached.
Thermodynamic favorability (relative stability), not rate. Energy difference determines equilibrium position, not how fast equilibrium is reached.
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Identify the more stable state on an energy diagram: higher energy or lower energy?
Identify the more stable state on an energy diagram: higher energy or lower energy?
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Lower energy is more stable. Systems naturally move toward states of minimum potential energy.
Lower energy is more stable. Systems naturally move toward states of minimum potential energy.
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What is the sign of $H$ if reactants are at $50,\text{kJ}$ and products are at $20,\text{kJ}$?
What is the sign of $H$ if reactants are at $50,\text{kJ}$ and products are at $20,\text{kJ}$?
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$\Delta H < 0$. Products are lower in energy than reactants.
$\Delta H < 0$. Products are lower in energy than reactants.
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Find $H$ if $H_{reactants}=80,\text{kJ}$ and $H_{products}=120,\text{kJ}$.
Find $H$ if $H_{reactants}=80,\text{kJ}$ and $H_{products}=120,\text{kJ}$.
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$\Delta H = +40,\text{kJ}$. $\Delta H = 120 - 80 = +40,\text{kJ}$
$\Delta H = +40,\text{kJ}$. $\Delta H = 120 - 80 = +40,\text{kJ}$
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Find $H$ if $H_{reactants}=150,\text{kJ}$ and $H_{products}=90,\text{kJ}$.
Find $H$ if $H_{reactants}=150,\text{kJ}$ and $H_{products}=90,\text{kJ}$.
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$\Delta H = -60,\text{kJ}$. $\Delta H = 90 - 150 = -60,\text{kJ}$
$\Delta H = -60,\text{kJ}$. $\Delta H = 90 - 150 = -60,\text{kJ}$
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Find $E_a$ (forward) if reactants are at $30,\text{kJ}$ and the peak is at $110,\text{kJ}$.
Find $E_a$ (forward) if reactants are at $30,\text{kJ}$ and the peak is at $110,\text{kJ}$.
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$E_a = 80,\text{kJ}$. $E_a = 110 - 30 = 80,\text{kJ}$
$E_a = 80,\text{kJ}$. $E_a = 110 - 30 = 80,\text{kJ}$
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Find $E_a$ (reverse) if products are at $20,\text{kJ}$ and the peak is at $95,\text{kJ}$.
Find $E_a$ (reverse) if products are at $20,\text{kJ}$ and the peak is at $95,\text{kJ}$.
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$E_a = 75,\text{kJ}$. $E_a = 95 - 20 = 75,\text{kJ}$
$E_a = 75,\text{kJ}$. $E_a = 95 - 20 = 75,\text{kJ}$
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Find $E_{a,reverse}$ if $E_{a,forward}=70,\text{kJ}$ and $\Delta H=-30,\text{kJ}$.
Find $E_{a,reverse}$ if $E_{a,forward}=70,\text{kJ}$ and $\Delta H=-30,\text{kJ}$.
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$E_{a,reverse} = 100,\text{kJ}$. $E_{a,reverse} = 70 - (-30) = 100,\text{kJ}$
$E_{a,reverse} = 100,\text{kJ}$. $E_{a,reverse} = 70 - (-30) = 100,\text{kJ}$
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