Chemical Reactions and Equations

During a lab experiment, a scientist numbers three beakers. Next, she pours 150 mL of  liquid into each beaker. Each liquid is different.Then, the scientist adds 5 g of white solid baking soda (NaHCO₃) to each beaker and stirs. She observes the results.
In which of the beakers does the scientist observe clear evidence of a chemical reaction?

• beaker 1 only
• beaker 2 only
• beaker 3 only
• beakers 1,2, and 3

Which of the following is a chemical reaction?

• Water freezes.
• Sugar dissolves in water.
• Salt and pepper are mixed in a dish.
• Iron rusts.

When two substances were combined, bubbles were produced and the temperature dropped.  This most likely means that:

• a chemical reaction took place
• the two substances had low boiling points
• one substance dissolved in the other
• the two substances are non-reactive

Before a chemical reaction, the total mass of two reactants is measured to be 40 grams.  After the reaction, what should be the total mass of the products?

• 0 grams
• 20 grams
• 40 grams
• 80 grams

Copper chloride and aluminum react to produce aluminum chloride and copper.  Which of the following is the correctly balanced chemical equation for this reaction?

• CuCl₂ + Al -> AlCl₃ + Cu
• 3CuCl₂ + Al -> AlCl₃ + 2Cu
• 3CuCl₂ + 2Al -> 2AlCl₃ + 3Cu
• CuCl₂ + 3Al -> AlCl₃ + 2Cu

Which observation would most likely indicate that an exothermic reaction has occurred?

• a color change
• the production of gas bubbles
• an increase in temperature
• a decrease in temperature

The first part of a balanced chemical equation is shown:  H₂SO₄ + 2NaOH → ________.  In order for this equation to be balanced, how many hydrogen (H) atoms must be present in the products?

• 2
• 3
• 4
• 5

Suppose two substances were combined together in a beaker. You know that a chemical reaction occurred if:

• new substances were created.
• one substance dissolved in the other.
• one substance melted in the other.
•  the two substances remained separate.

All of the following are indicators of a chemical reaction except one.  Which one is NOT an indicator that a chemical reaction has taken place?

• he production of heat or light
• a color change
• the production of gas bubbles
• the dissolving of one substance in another

 The idea that matter is neither created nor destroyed in chemical reactions is known as the:

•  The idea that matter is neither created nor destroyed in chemical reactions is known as the:
• law of conservation of energy.
•  law of conservation of mass.
• second law of thermodynamics.