gchemcalc: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gchemcalc - from package: gcu-bin

You may install the required package with command apt-get install {package}

Error in other languages:
gchemcalc: bevel nie gevind nie
gchemcalc: comandă negăsită
gchemcalc: comando não encontrado
gchemcalc: commande introuvable
gchemcalc: command not found
gchemcalc: käsku ei ole
gchemcalc: không tìm thấy lệnh
gchemcalc: komanda nerasta
gchemcalc: Kommando nicht gefunden.
gchemcalc: kommandot finns inte
gchemcalc: komut yok
gchemcalc: nie znaleziono polecenia
gchemcalc: níor aimsíodh an t-ordú
gchemcalc: no se encontró la orden
gchemcalc: no s'ha trobat l'ordre
gchemcalc: opdracht niet gevonden
gchemcalc: parancs nem található
gchemcalc: perintah tidak ditemukan
gchemcalc: príkaz nenájdený
gchemcalc: příkaz nenalezen
gchemcalc: команда не найдена
gchemcalc: командата не е открита
gchemcalc: 命令找不到
gchemcalc: コマンドが見つかりません