Physical and chemical changes, endothermic and exothermic reactions Flashcards
What is a physical change?
A physical change is a change in the physical property of a substance that is reversible, and where no bonds between atoms are broken, and no new substances are made.
eg. Melting, condensation, boiling, dissolving
What is a chemical change?
A change occurs when the bonds between atoms are broken, and atoms are rearrange to create new substances, usually irreversible.
eg. lighting a match, baking a cake, explosion, consuming food.
What are signs of a chemical reaction?
- Energy in the form of heat is either absorbed or produced
- Permanent colour change occurring (non-reversible)
- When a precipitate (powder) forms
- Gas produced- we can identify this if there are bubbles that have been formed or if a new/ unusual smell is observed from the reaction
- Energy in the form of light is produced eg. lighting a match
What is an exothermic reaction?
An exothermic reaction is one where more heat energy is being released when new bonds are formed, than is absorbed/taken in to break bonds.
This cause the temperature of the surroundings to increase (feel hot).
What is an endothermic reaction?
An endothermic reaction is one where more energy is being absorbed/taken in to break bonds than is released when new bonds are made.
This causes the temperature of the surrounding s to decrease (feel cold)
