2023 7th/8th Grade Midterm Review

Five grams of a white, solid chemical are added to 15 grams of water at a temperature of 22 degrees Celsius. Several observations are made. Which best indicates that a chemical reaction took place?

• calcium chloride remained in solution

• solution becomes lighter in color

• mass of the solution totals 20 grams

• temperature of solution is 35 degrees Celsius

This equation represents an unbalanced chemical reaction:

NaI + Cl_² ⟶  NaCl + I₂

When the equation is balanced, which coefficient should be placed before NaCl?

• 2

• 4

• 3

• 5

This is an unbalanced equation representing a chemical reaction:

HgO →  Hg + O₂

Which equation is the correctly balanced chemical equation for this reaction?

• HgO →  Hg + 2O₂

• 2HgO →  2Hg + O₂

• 2HgO →  Hg + O₂

• 2HgO →  Hg + 2O₂

A scientist combined baking soda and vinegar to demonstrate a chemical reaction. What indicates that one occurred?

• formation of bubbles

• disappearance of atoms

• reduction in total mass

• increase in number of atoms

. 

Which of the following is produced when 2 or more elements combine in a chemical reaction?

• atom

• mixture

• compound

• solution

A solution that contains less solute than it can hold at a given temperature is

• disassociated

• supersaturated

• saturated

• unsaturated

If a liquid is heated, what happens to both its energy content and the speed of its particles?

• energy increases; speed decreases

• energy remains the same, speed remains the same

• energy remains the same, speed increases

How is this reaction classified?

CaO + H₂O →  Ca(OH)₂ + heat

• endothermic

• decomposition

• exothermic

• double replacement

How does the total amount of matter before a chemical reaction compare to the total amount after the reaction?

• amount of matter is greater before the reaction

• amount of matter is greater after the reaction

• there is no relationship between the amount of matter before and after

• the amount of matter before and after the reaction is the same

Jessi is completing an investigation. She could conclude a chemical change is taking place if which of the following occurs?

• size gets smaller

• state of matter changes

• new substance forms