Jessi teaches Squeaks all about recycling, and together, they recycle his old crayons to make cool new ones! Second Grade Next Generation Science Standards Disciplinary Core Idea: PS1.B: Chemical Reactions - Heating or cooling a substance may cause changes that can be observed. Sometimes these changes are reversible, and sometimes they are not (2-PS1-4). Performance Expectation: 2-PS1-4 Construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot.