Conservation & Reactions

Which of the following is true of the Law of Conservation of Mass?

• The same number and type of each atom will always be present before and after a chemical reaction takes place.
• Some of the atoms present before the reaction will always be lost during a chemical reaction.
• Some of the atoms will always be changed into a different type of atom by a chemical reaction.
• During a chemical reaction, atoms will always be combined into much larger molecules.

Which of the following is the best description of the results of a chemical reaction?

• The substance seems to disappear after dissolving in water.
• The substance changes from liquid to solid at a low temperature.
• The reaction can be reversed to get back the original substance.
• A new substance with different properties is formed.

Which of the following is a chemical change?

• Baking soda and vinegar producing gas bubbles
• A chocolate bar melting
• Powdered lemonade dissolving in water
• Frosting a cake

An oreo cookie has a mass of 20 grams. It gets crushed into crumbs for a recipe. What is the mass of the crumbs?

• 15 grams

• 25 grams

• 20 grams

• 10 grams

If reaction starts with 25g of reactants, it will produce --

• a total of 50g of product

• a total of 5g of product

• a total of 80 g of product

• a total of 25g of product

How many of each type of atom are in the formula NH₃?

• 1 nitrogen, 3 hydrogen

• 3 nitrogen, 3 hydrogen

• 1 neon, 3 hydrogen

• 1 nitrogen, 3 helium

How many molecules are represented in the formula 3CO₂?

• 3 carbon, 2 oxygen

• 6 carbon dioxide

• 3 carbon dioxide

• 3 carbon, 6 oxygen

What will have more mass when a chemical change is complete: the reactants before the chemical reaction or the product after the reaction is complete?

• They both will have the same mass

• The product always has more mass than the reactant

• The reactant will have more mass than the product

• They both will lose mass after the reaction

If there are 4 H atoms on the reactant side, how many H atoms will be on the product side? 

• 2
• 4
• 6
• You need more information to answer this question

How many atoms of Aluminum (Al) are on each side of the following equation?

4Al + 3O₂ --> 2Al₂ O₃

• 2

• 6

• 1

• 4