Flexi Says: Bubbles produced when mixing substances can be a sign of a chemical change. A chemical change occurs when matter changes into an entirely different substance. The new substance has different properties. Bubbles may form when a gas is produced from substances that were liquid or solid at room temperature. For example, when vinegar and baking soda combine, they form carbon dioxide. Carbon dioxide is a gas at room temperature. It is this gas that causes the bubbles.