"Still not done?"
Toma peered into the test tube. Thirty minutes had passed, but the reaction hadn't started.
"Too slow," Kana said with dissatisfaction.
Rei calmly answered. "Reaction rate is determined by various factors."
"Then why is this one slow?"
"Probably high activation energy. The energy barrier needed for the reaction."
Toma tilted his head. "Barrier?"
Rei drew a diagram. A mountain-like curve. "To go from reactants to products, you must climb an energy mountain. The peak is the transition state."
"Mountain climbing?" Kana became interested.
"Yes. If you raise the temperature, molecular kinetic energy increases, making it easier to cross the mountain."
Toma immediately reached for the heater.
"Wait," Rei stopped him. "Rapid heating is dangerous. Besides, it's not a method usable for biological reactions."
"Then how do living things do it? Body temperature is constant, yet reactions are fast."
Rei smiled. "Enzymes. They work as catalysts."
"Catalysts?"
"Substances that speed up reactions but don't change themselves. They lower activation energy."
Kana wrote in her notebook. "Lowering the mountain?"
"More precisely, creating another lower path. Like a tunnel."
Toma got excited. "Amazing! So if we add enzymes, it'll speed up?"
"In theory. But there's the issue of substrate specificity."
"Substrate specificity?"
Rei continued explaining. "Enzymes only act on specific molecules. A lock and key relationship."
Kana twirled her pen while thinking. "Whether an enzyme exists for this reaction..."
"Probably not. It's an artificial reaction."
Toma sighed. "Then what can we do?"
"Increase concentration. If reactant concentration is high, collision frequency between molecules increases."
"But we already added the maximum amount."
Rei looked at the test tube. "pH is also important. Hydrogen ion concentration affects reaction rate."
Kana looked at the reagent shelf. "Add acid?"
"Carefully. Little by little."
Toma added one drop of acid with a pipette. They waited. Nothing happened.
"No good."
Rei pondered. "Maybe surface area."
"Surface area?"
"For solid-liquid reactions, larger solid surface area means faster reactions. More contact area."
Kana shook the test tube. "Should we mix?"
"Stirring is effective. But in this case, both are liquids..."
Toma suddenly thought. "What if there's an inhibitor?"
Rei's eyes lit up. "Sharp. Impurities can sometimes interfere with reactions."
"Then how do we check?"
"Try with new reagents or purify."
Kana prepared a new test tube. Rei carefully mixed the reagents.
This time, the color began changing immediately.
"Fast!" Toma shouted.
"It was impurities after all. Probably metal ions acting as catalyst poison."
Kana took notes. "Catalyst poison?"
"Substances that stop catalyst function. Same thing happens with enzymes."
Toma compared it with the old test tube. "Such a difference."
Rei organized. "Reaction rate depends on temperature, concentration, catalysts, pH, surface area, inhibitors... many factors."
"It's complex," Kana murmured.
"That's why life can control precisely. Reactions occur at the needed speed when needed."
Toma's face showed understanding. "It wasn't anyone's fault it was slow. It was the conditions."
"Lesson from the experiment," Rei said. "Don't rush results, verify factors one by one."
Two test tubes stood side by side. One stationary, one actively changing. The same reaction, completely different speeds depending on conditions.
"Chemistry is more delicate than I thought," Kana admired.
Rei nodded. "And that makes life possible."