A reaction energy diagram for a single-step reaction shows a curve that rises from the reactants to a highest point, then falls to the products. What does the highest point (the peak) represent?
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A reaction energy diagram for a single-step reaction shows a curve that rises from the reactants to a highest point, then falls to the products. What does the highest point (the peak) represent?
A reaction energy diagram for a single-step reaction shows a curve that rises from the reactants to a highest point, then falls to the products. What does the highest point (the peak) represent?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! The highest point (peak) on the curve represents the TRANSITION STATE or ACTIVATED COMPLEX—this is the unstable, high-energy arrangement where old bonds are partially broken and new bonds are partially formed, like a molecular "halfway point" during the reaction. Choice B correctly identifies the peak as the transition state (activated complex), the highest-energy point where the reacting molecules are in their most unstable configuration as bonds rearrange. Choice A incorrectly identifies the products as the highest point—products are at the END of the reaction (right side) and can be either higher or lower than reactants, but never at the peak. Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
A single-step energy profile is drawn with Energy on the y-axis and Reaction progress on the x-axis. The curve starts at the reactants, rises to one peak, then falls to the products. Which diagram feature shows the overall energy change (ΔH)?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! The overall energy change ΔH is shown by the vertical difference between reactant and product levels, regardless of the peak. Choice A correctly interprets the energy diagram by identifying the reactant-product difference as ΔH. Choice D fails by using horizontal distance—that's reaction progress, not energy; energy is vertical! Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
A single-step reaction energy diagram shows reactants at 90 kJ, a peak at 140 kJ, and products at 120 kJ. Which statement is correct?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! With reactants at 90 kJ, peak at 140 kJ, and products at 120 kJ: ΔH = 120 - 90 = +30 kJ (positive), meaning products are HIGHER than reactants—energy must be absorbed, making this ENDOTHERMIC. Choice B correctly identifies the reaction as endothermic because the products (120 kJ) are higher in energy than the reactants (90 kJ), requiring net energy absorption. Choice A incorrectly claims the reaction is exothermic just because the peak is above reactants—ALL reactions have peaks above reactants (that's activation energy), but exo/endo depends on whether products end up higher or lower than reactants. Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
A reaction energy diagram (single-step) shows reactants on the left, products on the right, and one peak in between. What does the peak represent?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! In a single-step diagram, the peak is the transition state, the unstable high-energy point where old bonds break and new ones form. Choice C correctly interprets the energy diagram by identifying the peak as the transition state (activated complex). Choice A fails by confusing the peak with products—products are the stable endpoint on the right, while the peak is the temporary high point in the middle. Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume 'upward curve' means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors. You're making fantastic progress!
A single-step energy diagram shows reactants at 90 kJ, a peak at 160 kJ, and products at 50 kJ. Which statement correctly describes the overall energy change ΔH?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! Here, products at 50 kJ are lower than reactants at 90 kJ, so ΔH = 50 - 90 = -40 kJ, negative. Choice B correctly interprets the energy diagram by measuring from reactants to products and noting the negative ΔH. Choice A fails by focusing on the peak being above reactants—that's activation energy, not ΔH; remember to compare endpoints for overall change. Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume 'upward curve' means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors. You're on a roll—fantastic!
A single-step reaction energy diagram shows reactants at 50 kJ and products at 90 kJ (with one peak in between). Which statement about the overall energy change (ΔH) is correct?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! With reactants at 50 kJ and products at 90 kJ, the overall energy change ΔH = products - reactants = 90 - 50 = +40 kJ, which is POSITIVE, indicating an ENDOTHERMIC reaction where energy is absorbed from the surroundings to raise products to a higher energy level than reactants. Choice B correctly identifies this as endothermic with positive ΔH because products (90 kJ) are at a higher energy than reactants (50 kJ), meaning energy must be absorbed during the reaction. Choice A incorrectly calls it exothermic, Choice C wrongly links the presence of a peak to being exothermic (all reactions have peaks!), and Choice D incorrectly claims ΔH = 0. Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. For this problem: products (90 kJ) > reactants (50 kJ), so ENDOTHERMIC!
Consider this single-step energy diagram: reactants at 70 kJ, peak at 120 kJ, products at 70 kJ. What is the overall energy change (ΔH) for the reaction based on the diagram?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! In this case, reactants and products both at 70 kJ (peak at 120 kJ), so ΔH = 70 - 70 = 0 kJ, meaning no net energy change. Choice C correctly interprets the energy diagram by recognizing ΔH is zero when levels are the same. Choice D fails by equating ΔH to Ea—Ea is reactants to peak (50 kJ), but ΔH is reactants to products (0 kJ)! Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
An energy profile for a single-step reaction is shown (Energy on the y-axis, Reaction progress on the x-axis). The curve starts at the reactants at about 90 kJ, rises to a peak at about 150 kJ (transition state), then drops to the products at about 50 kJ. Based on this diagram, is the reaction exothermic or endothermic?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! In this diagram, the reactants are at 90 kJ, the peak at 150 kJ, and products at 50 kJ, so ΔH = 50 - 90 = -40 kJ (negative, exothermic) since products are lower. Choice B correctly interprets the energy diagram by noting the products are at lower energy than reactants, indicating an exothermic reaction. Choice A fails by confusing the initial rise (activation) with the overall change—remember, all reactions rise to a peak, but exo/endo depends on endpoints! Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
A single-step reaction energy diagram has reactants at 100 kJ, a peak at 160 kJ, and products at 140 kJ. Based on the diagram, which statement is correct?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! In this diagram, reactants are at 100 kJ and products at 140 kJ, so products are higher, making the reaction endothermic. Choice B correctly interprets the energy diagram by stating the reaction is endothermic because products are at higher energy than reactants. Choice C fails because the activation energy is from reactants to peak (60 kJ), not the drop from peak to products (20 kJ). Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.
Two single-step reaction energy diagrams have the same reactant and product energy levels, but Diagram 1 has a higher peak than Diagram 2. Which statement is true?
Explanation: This question tests your ability to interpret reaction energy diagrams that show how energy changes as a reaction proceeds from reactants to products, including identifying activation energy and determining whether the reaction is exothermic or endothermic. A reaction energy diagram plots energy (y-axis) against reaction progress (x-axis, showing the journey from reactants on left to products on right): the curve starts at the reactant energy level, rises to a peak (the transition state—highest energy point as bonds are breaking and forming), then descends to the product energy level. Two key measurements come from this diagram: (1) ACTIVATION ENERGY is the height from the reactant level UP to the peak (the energy barrier that must be overcome to start the reaction—like pushing a boulder uphill), and (2) OVERALL ENERGY CHANGE (ΔH) is the height difference between reactants and products (positive if products higher = endothermic, negative if products lower = exothermic). The activation energy tells you how hard it is to START the reaction, while the overall change tells you whether energy is released or absorbed OVERALL! Since both diagrams have the same reactant and product levels, ΔH is identical, but Diagram 1's higher peak means larger activation energy. Choice A correctly interprets the energy diagrams by noting that Diagram 1 has a larger activation energy due to its higher peak. Choice B fails because ΔH is the same for both since reactant and product levels match—only the peak differs. Reading energy diagrams—the three-level method: (1) LOCATE REACTANTS (starting point, left side): note their energy level height. (2) LOCATE PEAK (highest point on curve): note its height. Activation energy = peak height MINUS reactant height (the climb from start to top). (3) LOCATE PRODUCTS (ending point, right side): note their energy level. Overall energy change = product height MINUS reactant height (positive if products higher, negative if products lower). Determine exo/endo: products LOWER than reactants (energy drops, released) = EXOTHERMIC. Products HIGHER than reactants (energy rises, absorbed) = ENDOTHERMIC. This three-level reading (reactants, peak, products) gives you everything! Common diagram-reading mistakes to avoid: (1) DON'T measure activation energy from the x-axis to peak—measure from REACTANT LEVEL to peak! The absolute height doesn't matter; it's the climb from where you start. (2) DON'T confuse activation energy with overall energy change—activation is about the barrier (reactants to peak), overall is about net change (reactants to products). A reaction can have HIGH activation energy (hard to start, tall peak) but be EXOTHERMIC overall (products lower, releases energy)—common for combustion! (3) DON'T assume "upward curve" means endothermic—ALL reactions go up to the peak first (activation), then what matters is whether products end up higher or lower than reactants. Check the endpoints, not just the middle! These three checks prevent most diagram errors.