Valerie Leonard, left, and Katie deBuys in “The How and The Why” at Theater J. (C. Stanley Photography)

Sometimes a two-person play is like a chemistry experiment — one of those laboratory feats that yield changing colors, erupting textures and whiffs of smoke coiling up from the test tubes. Certainly, when you watch two gripping productions of contemporary two-actor works — Sarah Treem’s “The How and the Why” at Theater J, and Jane Martin’s “H20” at Rep Stage — you can almost imagine each playwright donning safety glasses and announcing: “I’m going to fling together two combustible characters and worldviews. Stand back! We’ll see what happens.”

In the smart, taut “The How and the Why,” an encounter between two scientists precipitates a war of ideas and treacherous emotion. The young graduate student Rachel (Katie deBuys) has much in common with the older professor Zelda (Valerie Leonard): Both women are brilliant, ambitious evolutionary biologists. Each has come up with a theory that could revolutionize ideas about how women’s physiology affects society. But when the two scientists’ careers intersect on the eve of a big conference, each decision and shared confidence may open the door to betrayal.

The tension runs high from the initial moments of director Shirley Serotsky’s suspenseful yet often funny production. DeBuys’s Rachel is a ticking time bomb of nerves and resentment; Leonard’s calm, arrogant Zelda betrays hints of vulnerability. Set designer Paige Hathaway’s evocation of Zelda’s plush university office emphasizes the early power imbalance between the characters; later, as the relationship changes, the office morphs into a bar.

The co-creator and showrunner of Showtime’s “The Affair,” and a past writer for HBO’s “In Treatment” and Netflix’s “House of Cards,” Treem movingly depicts two characters who burn with passion for ideas but struggle to understand each other’s attitudes and choices. The portrait of female scientists fighting for professional recognition and personal contentment has obvious resonance at a time when protesters have defiantly embraced the insult “nasty woman” and a “March for Science” is in the works. But “The How and the Why” also reflects broadly on the nature of social bonds and the perspective that’s gained with aging.

Whereas Treem’s characters belong to the same scholarly circle, the protagonists in “H20” represent drastically different worlds. Deborah (Krenée A. Tolson) is a fervent evangelical Christian who’s eking out a living as an off-off-Broadway actor. Jake (Robbie Gay) is a pessimistic, foul-mouthed action-movie star who is as self-destructive as he is rich. After the two cross paths, as Jake prepares to play Hamlet on Broadway, he decides that only Deborah can portray his Ophelia. The duo’s contentious relationship teeters on the brink of romance leading up to opening night, an occasion that may offer Jake a last chance at meaning and redemption.

Robbie Gay as Jake and Krenée A. Tolson as Deborah in “H2O” at Rep Stage. (Katie Simmons-Barth)

In the affecting and fluidly paced Rep Stage production, directed by Kasi Campbell, Gay is terrific as the despairing, dissolute, sardonic Jake, while Tolson delivers a believable portrait of the determined, feisty Deborah. These two people may be representatives of America’s ongoing culture wars — religious traditionalism vs. modern secularism, high culture vs. pop culture — but they are memorable individuals first. (Ben Argenta Kress designed the character-appropriate costumes. Daniel Ettinger designed the spare set.)

As befits a work that acknowledges the thrill and power of theater, “H20” is full of metatheatrical touches: Amid the flow of brief, snappy scenes, Jake and Deborah often address the audience directly, and most costume changes are done onstage, with assistance from stagehands. Campbell’s in-the-round staging complements this conceit. A downside is that, occasionally, a performer’s back will be turned to you just when you yearn to see his or her expression. That’s a shame, since, in such an intimate study of two clashing wills, every second counts.

The How and the Why by Sarah Treem. Directed by Shirley Serotsky; lighting design, Martha Mountain; costumes, Danielle Preston; sound, Justin Schmitz; properties, Kevin Laughon. About 2 hours. Through March 12 at Theater J, 1529 16th St. NW. Tickets $30-$64. Call 202-777-3210 or visit theaterj.org.

H2O by Jane Martin. Directed by Kasi Campbell; light design, Dan Covey; sound, Neil McFadden; properties, Mollie Singer; associate light design, William D’Eugenio. About 1 hour 40 minutes. Through March 5 at the Horowitz Visual and Performing Arts Center on the campus of Howard Community College, 10901 Little Patuxent Pkwy., Columbia, Md. Tickets: $15-40. Call 443-518-1500 or visit repstage.org.