Based on their descriptions, classify these chemical changes as endothermic or exothermic.
1) a chemical change takes place in a container, making it feel cold to touch.
2) burning wood
3) a chemical change takes place in a container, making it feel hot to touch.
4) pocket hand warmers(used by skiers) start out at room temperature. when you open the air tight packaging, a substance reacts with air, and it quickly begins to feel hot.
5) a "cold pack" (used for sport injuries) starts out a room temperature. but when you squish the liquid around, you cause two substances to mix that were originally kept separate. those substances react and the pack begins to feel cold.

1) endothermic

2) exothermic

3) exothermic

4) exothermic

5) endothermic

Explanation: An endothermic reaction is a type of of chemical reaction in which energy is absorbed from the surrounding. The temperature of the surrounding decreases.

An Exothermic reaction is a type of of chemical reaction in which energy is released into the surrounding. The temperature of the surrounding increases.

1) A chemical change takes place in a container, making it feel cold to touch: When an endothermic reaction takes place in the container, the temperature of the surrounding (here the outside wall of the container) will decrease which can be felt by touching the outside of the container.

2) Burning wood: Burning of wood is an example of exothermic reaction because energy is releases into surroundings.

3) A chemical change takes place in a container, making it feel hot to touch : When an exothermic reaction takes place in the container, the temperature of the surrounding (here the outside wall of the container) will increase which can be felt by touching the outside of the container.

4) Pocket hand warmers(used by skiers) start out at room temperature. When you open the air tight packaging, a substance reacts with air, and it quickly begins to feel hot: When an exothermic reaction takes place in the container, the temperature of the surrounding (here the outside wall of the hand warmer) will increase which can be felt by touching the outside of the warmer.

5) A "cold pack" (used for sport injuries) starts out a room temperature. But when you squish the liquid around, you cause two substances to mix that were originally kept separate. Those substances react and the pack begins to feel cold:  When an endothermic reaction takes place in the cold pack, the temperature of the pack will decrease which can be felt by touching the outside of the pack.

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

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