George Thomson Armstrong, 65, a physical chemist with the National Bureau of Standards since 1951 and editor of the international Journal of Chemical Thermodynamics, died March 9 at Holy Cross Hospital after a heart attack. He lived in Silver Spring.

Dr. Armstrong was a native of Alberta, Canada. He earned his doctoral degree at Johns Hopkins University in 1948. From 1945 until 1951, he taught at Yale University, Boston University, and Johns Hopkins.

He moved to Washington in 1951 when he joined the National Bureau of Standards. He received the Commerce Department's Silver Medal award in 1967.

Dr. Armstrong was a former committee chairman for the American Society for Testing Materials, chairman of the U.S. Calorimetry Conference, and president of the Washington Philosophical Society. He was a fellow of the American Physical Society, the Washington Academy of Sciences, and the American Association for the Advancement of Science.

He was a member of the Cosmos Club, St. Andrew's Society, the Potomac Appalachian Trail club, and Christ Congregational Church in Silver Spring.

Survivors include his wife, Patricia C., of Silver Spring; a daughter, Margaret A. Chapman of Houston, Tex.; a son, Michael F., of Annapolis; a sister, Jean A. Carty of Miami; a brother, Wallace F., of Baton Rouge, La., and two grandchildren.