Chemical Reactions

A chemical reaction is a process in which

• all reactants change state

• products change into reactants

• the law of conservation of mass applies

How can a chemical equation be balanced?

• changing subscripts

• erasing elements as necessary

• adding coefficients

• adding elements as necessary

What are the products in the equation?

• Zn and CuSO₄

• Zn and Cu

• ZnSO₄ and Cu

• Zn only

The following are the evidences that chemical reaction took place, EXCEPT:

• evolution of gas

• formation of precipitate

• formation of new element

• change in the intrinsic properties

What type of reaction is present in the unbalanced equation, NaOH + KNO₃ ---> NaNO₃ + KOH

• combination

• decomposition

• double replacement

• combustion

What type of reaction is present in the unbalanced equation, Fe + NaBr --> FeBr₃ + Na

• combustion

• single replacement

• double replacement

• acid-base

Which of the following best describes the combustion reaction?

• hydrocarbon combines with oxygen to produce CO₂ and H₂O

• hydrogen combines with CO₂ to produce O₂ and H₂O

• hydrocarbon combines with H₂O to produce CO₂ and O₂

• CO₂ combines with oxygen to produce hydroxide and H₂O

Chemical equations are balanced by placing the appropriate

___________ before the symbols or formulas of reactants and

products.

• subscript

• exponent

• letter

• coefficient

Which of the following is the balanced equation for Zn + HCl --> ZnCl2 + H2?

• Zn + HCl --> 2ZnCl₂ + H₂

• Zn + 2HCl --> ZnCl₂ + H₂

• 2Zn + HCl --> 2ZnCl₂ + H₂

• Zn + 2HCl --> 2ZnCl₂ + H₂

Which of the following sets of coefficients can be used to balance the equation, CH4 + O2 --> CO2 + H2O

• 1,1,2,1,

• 1,2,1,2

• 2,1,2,1

• 2,2,1,1