Law of Conservation of Mass

1. The equation below represents a chemical reaction that occurs in living cells.
   
   $\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy}$
   
   How many atoms are represented in the reactants of this equation?

1. In which of these compounds are there twice as many oxygen atoms as hydrogen atoms?

1. Some students are using samples of different substances for a lab investigation. They plan to observe the physical properties of each substance and record their observations in a table.
   
   Data Table
   Sample 1: S
   Sample 2: $\mathrm{N_2O_4}$
   Sample 3: Fe
   Sample 4: $\mathrm{O_2}$
   Sample 5: LiF
   Sample 6: Sr
   Sample 7: Al
   
   Which of the substances observed are elements?

1. Strontium phosphate, $\mathrm{Sr_3(PO_4)_2}$, is a crystalline substance used in medicine and industry. How many phosphorus atoms are represented in the formula for $\mathrm{Sr_3(PO_4)_2}$?

1. A chemical reaction in which calcium carbonate, $\mathrm{CaCO_3}$, is decomposed results in the production of two simpler compounds.
   
   $\mathrm{CaCO_3 \rightarrow CaO + CO_2}$
   
   $\mathrm{CaCO_3}$ ? g     $\mathrm{CaO}$ 28.00 g     $\mathrm{CO_2}$ 21.97 g
   
   What mass of calcium carbonate, to the nearest hundredth of a gram, is decomposed in this reaction?

1. The table shows the chemical formulas for four substances.
   
   1: $\mathrm{C_2H_6O}$
   2: $\mathrm{C_8H_{18}}$
   3: $\mathrm{CH_3CH_2Br}$
   4: $\mathrm{C_4H_{10}O}$
   
   Which substances have the same number of carbon atoms?

$\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}$

How many different elements are involved in the reaction shown above?

How many atoms of oxygen are in one molecule of glucose, $\mathrm{C_6H_{12}O_6}$?

A teacher asks a student to write the chemical equation for photosynthesis. The student’s response is shown below.

$\mathrm{CO_2 + H_2O \xrightarrow{light} C_6H_{12}O_6 + O_2}$

The equation is not balanced correctly. Which of these is a balanced equation for photosynthesis?

The chemical equation shown below represents a reaction that can produce hydrogen fuel for certain cars.

$\mathrm{CO + H_2O \rightarrow CO_2 + H_2}$

Which substance represented in this equation is classified as an element?

In the chemical reaction shown below, the products are best classified as—

$\mathrm{CaCO_3 \xrightarrow{heat} CaO + CO_2}$

The chemical formula for sodium sulfate is $\mathrm{Na_2SO_4}$. How many sulfur atoms are in one formula unit of sodium sulfate?

Serotonin is a chemical substance that acts as a neurotransmitter. The formula for one molecule of serotonin is shown below.

$\mathrm{C_{10}H_{12}N_2O}$

How many atoms total are in one molecule of serotonin?

All of the following reactions are correctly balanced except—

Which of these formulas contain equal numbers of nitrogen atoms?

I. $\mathrm{Co(NO_3)_2}$ II. $\mathrm{(NH_4)_2CO_3}$ III. $\mathrm{(NH_4)_3PO_4}$ IV. $\mathrm{Al(NO_3)_3}$ V. $\mathrm{NH_4NO_3}$