"Still not finished..."
Toma looked at the clock.
Kana peeked in. "What reaction?"
"Esterification. Been waiting three hours already."
Rei smiled wryly. "Can't control reaction rate."
"Can't control?" Toma said dissatisfied.
"Can influence it. But basic rate is determined by reaction nature."
Kana opened her notebook. "What determines rate?"
Rei wrote on the whiteboard. "Concentration, temperature, catalyst, and reaction mechanism."
"Concentration makes sense. Denser means faster," Toma said.
"Collision frequency increases," Rei explained.
"Temperature?" Kana asked.
"Higher is faster. Molecular motion becomes active."
Toma tried to heat the experiment. "Then I'll raise temperature."
"Wait," Rei stopped him. "Side reactions might occur."
"Side reactions?"
"Reactions other than intended. Undesirable products form."
Kana noted. "So endure at appropriate temperature?"
"Yes. Biochemical reactions are especially temperature-sensitive. Enzymes denature."
Toma made a resigned face. "Then catalysts?"
"That's the key," Rei emphasized. "Catalysts dramatically increase reaction rate."
"How much?"
"Enzymes can do million times or billion times."
Kana was surprised. "Billion times?"
"Catalase enzyme. Catalyzes hydrogen peroxide decomposition over million times per second."
Toma became interested. "Why so fast?"
Rei drew a diagram. "Because it lowers activation energy."
"Activation energy?"
"Minimum energy needed for reaction to occur. Like crossing a mountain."
Kana tried to understand. "Mountain?"
"Between reactants and products, there's an energy mountain. Must cross it to react."
Toma asked. "Catalyst lowers that mountain?"
"Correct. Provides alternate route to bypass the mountain."
Rei explained in detail. "Enzyme binds substrate specifically. Forms enzyme-substrate complex."
"Complex?"
"Temporary bonded form. Environment where reaction occurs easily is created there."
Kana drew in notebook. "E + S → ES → E + P."
"Perfect. E is enzyme, S is substrate, P is product."
Toma questioned. "Enzyme isn't consumed?"
"Not consumed. That's why it's a catalyst. Can be used many times."
"Convenient."
Rei continued. "But enzymes have high substrate specificity."
"Specificity?"
"Only works on specific substrates. Key and lock relationship."
Kana asked for examples. "For instance?"
"Amylase breaks down starch. But doesn't work on protein."
Toma had another question. "What happens without enzyme?"
"Reaction is too slow at body temperature. Can't digest or metabolize."
Rei gave a concrete example. "Sucrose hydrolysis. Without enzyme, takes years."
"Years?" Kana was surprised.
"But with sucrase enzyme, takes seconds."
Toma admired. "Life can't exist without enzymes."
"Exactly. Thousands of enzyme types work in the body."
Kana had a doubt. "But enzyme speed also has limits?"
Rei nodded. "Michaelis-Menten equation. When substrate concentration gets high, rate plateaus."
"Why?"
"Enzyme saturates. When all enzymes are bound to substrate, can't get faster."
Toma made a metaphor. "When all cash registers are full, even if customers increase, processing speed doesn't change?"
"Good analogy," Rei acknowledged.
Kana remembered another factor. "Inhibitors?"
"Substances that slow reaction. There's competitive and non-competitive inhibition."
"Competitive?"
"Competes with substrate to bind enzyme active site."
Rei continued. "Non-competitive inhibition binds elsewhere and changes enzyme shape."
Toma asked for practical examples. "Drugs are inhibitors?"
"Many drugs are enzyme inhibitors. Aspirin inhibits cyclooxygenase."
"Pain reliever."
"Yes. Suppresses production of inflammation-causing substances."
Kana was moved. "Controlling reaction rate becomes medicine."
Rei nodded. "Many life phenomena depend on enzyme rate control."
Toma looked at his experiment. "So this slow reaction?"
"No catalyst. Natural rate."
"If I add enzyme?"
Rei shook his head. "Few enzymes suitable for chemical synthesis. Industry uses metal catalysts."
Kana understood. "Enzymes for biological reactions, metal catalysts for chemical synthesis."
"Roughly speaking."
Toma stood up. "So I just have to wait?"
"Patience," Rei laughed.
"Slow reaction rate isn't anyone's fault."
Kana smiled. "It's chemistry's law's fault."
The three laughed. Reactions proceed at their own pace.