A grenade/mortar explosion will cause severe internal bleeding and organ damage/failure, most soliders that are in the proximity of an explosion will either die of shrapnel wounds or internal bleeding.
If Ukraine were using chemical weapons (of which there's been no evidence in the war so far and would work against their desire to join NATO), it would involve larger scale attacks. Dropping tiny amounts on a couple of soldiers makes no sense.
I can show you some thermite videos the Russians have been dropping all over cities (that apparently 'voted' to be part of Russia). Thermite burns uncontrollably and will go through your clothing and skin. They're also using thermobaric bombs, that suck all the air out of the area and cause a violent shockwave. Again used against civilian areas. Both are vile weapons that no civilised country should ever use against people they're alledgedly trying to 'save'.
I'm happy to share some neutral accounts reporting on the war, I follow both sides' reporting to try to make sense of what's actually happening. Ukrainian supporters tend to sometimes hide bad news for morale (which makes sense, they're fighting one of the largest armies in the world on their own) and Russians spread lies (like the forced recruitment videos being shared), so it's not easy to know where to look.
FYI I'm a pacifist at heart, I hate the concept of war. As a species we should be past it by now, but there will always been scum like Putin launching genocidal wars of land conquest, which means we're stuck with wasted resources on military equipment and disruptions to the rest of the world.