“…The difficulty in understanding the meaning of the relatively huge number of abstract concepts, such as heat, energy, temperature, specific heat and bond energy (Spice 1966, Zemansky 1970, Erickson 1976, Karplus 1977, Strauss 1977, Treptow 1978, Anderson 1980, McCullough 1980, Rosenquist et al 1982, Hewson and Hamlyn 1984, Gayford 1986. The molecular-level explanation needed to understand these concepts is not easy for most students.…”