If a reaction has a very low activation energy, the products would be expected to form quickly at high temperatures. Select the reason why such a reaction might form products very slowly, or not at all? positive Δ G negative Δ G lack of a catalyst

An electron moved from shell n = 2 to shell n = 1. what most likely happened during the transition? a fraction of a photon was added. a photon of energy was absorbed. a fraction of a photon was removed. a photon of energy was released.

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.