Question

exit ticket — chemical combining of substances
name: madison crance
period: 4
date: oct 7th
grade:11

1. circle the sign of a chemical reaction you observed:

● color change gas bubbles precipitate temperature change

1. true or false: mass is always conserved in a chemical reaction.

□ true □ false

1. balance this equation:

h2 + o2 → h2o
balanced:

1. give one example of a chemical reaction you have seen:
2. in one sentence, explain how a chemical change is different from a physical change:

Explanation:

Step1: Identify chemical - reaction signs

Any of color change, gas bubbles, precipitate, temperature change can be circled depending on the observation.

Step2: Recall mass - conservation law

According to the law of conservation of mass, mass is always conserved in a chemical reaction. So the answer is True.

Step3: Balance the equation

We start with $H_2 + O_2
ightarrow H_2O$. There are 2 oxygen atoms on the left - hand side and 1 on the right - hand side. To balance the oxygen, we put a 2 in front of $H_2O$, getting $H_2+O_2
ightarrow 2H_2O$. Now there are 4 hydrogen atoms on the right - hand side and 2 on the left - hand side. So we put a 2 in front of $H_2$. The balanced equation is $2H_2 + O_2
ightarrow 2H_2O$.

Step4: Provide a chemical - reaction example

One example is the rusting of iron: $4Fe + 3O_2
ightarrow 2Fe_2O_3$.

Step5: Differentiate chemical and physical change

A chemical change results in the formation of new substances with different chemical properties, while a physical change only alters the physical state or appearance of a substance without changing its chemical composition.

Answer:

1. (Circle one based on observation)
2. True
3. $2H_2 + O_2

ightarrow 2H_2O$

1. Rusting of iron ($4Fe + 3O_2

ightarrow 2Fe_2O_3$)

1. A chemical change forms new substances with different chemical properties, while a physical change only changes physical state or appearance without altering chemical composition.