18. which of the following is an example of a physical change in matter?\na two substances produce heat when…

18. which of the following is an example of a physical change in matter?\na two substances produce heat when mixed b digestion of food\nc smash a watermelon with a hammer d cooking a waffle\n19. which of the following is an example of a chemical change in matter?\na campfire b sugar dissolving in water\nc inflating a tire d melting ice\n20. which of the following is a sign that a chemical change has occurred?\na dissolving b produces a gas\nc change in shape d melting

18. which of the following is an example of a physical change in matter?\na two substances produce heat when mixed b digestion of food\nc smash a watermelon with a hammer d cooking a waffle\n19. which of the following is an example of a chemical change in matter?\na campfire b sugar dissolving in water\nc inflating a tire d melting ice\n20. which of the following is a sign that a chemical change has occurred?\na dissolving b produces a gas\nc change in shape d melting

Answer

Brief Explanations:

  1. For question 18: A physical change alters the form or appearance of matter without changing its chemical composition. Smashing a watermelon with a hammer only changes its physical state (shape and size), while the other options involve chemical reactions.
  2. For question 19: A chemical change results in the formation of new substances with different chemical properties. A camp - fire involves combustion, a chemical reaction. Sugar dissolving in water is a physical change (dissolution), inflating a tire is a physical process of adding air, and melting ice is a physical change of state.
  3. For question 20: Producing a gas is a common sign of a chemical change as new substances are formed and release gases. Dissolving, change in shape, and melting are physical changes.

Answer:

  1. C. Smash a watermelon with a hammer
  2. A. Campfire
  3. B. Produces a gas