Question 1

A welder uses acetylene ($$\mathrm{C_2H_2}) $$and oxygen ($$\mathrm{O_2$}) to $$weld metals. If 50.0 g of acetylene is combusted, how many grams of carbon dioxide ($$\mathrm{CO_2$}) $$are produced? The balanced equation is: $$\mathrm{2C_2H_2 + 5O_2 \rightarrow 4CO_2 + 2H_2O}. ($$Molar masses: $$\mathrm{C_2H_2} = 26.0 g/$$mol, $$\mathrm{CO_2$} = 44.0 g/$$mol)

Accepted Answer

169 g

Question 2

Which of the following best describes an exothermic reaction?

Accepted Answer

Heat is released and the energy of the products is less than the reactants.

Question 3

A reaction produces 13.1 g of water ($$\mathrm{H_2O}). $$How many grams of oxygen ($$\mathrm{O_2$}) $$were used? The balanced equation is $$\mathrm{2H_2 + O_2$ \rightarrow 2H_2O}. ($$Molar mass $$\mathrm{H_2O} = 18.0 g/$$mol, $$\mathrm{O_2$} = 32.0 g/$$mol)

Accepted Answer

3.64 g

Question 4

Which factor will increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst

Question 5

In a thermite reaction used to weld railroad tracks, which statement is true?

Accepted Answer

The reaction is exothermic and releases heat.

Question 6

A student wants to produce 45.8 g of ammonia ($$\mathrm{NH_3$}) $$from nitrogen ($$\mathrm{N_2$}). $$How many grams of nitrogen are needed? The balanced equation is $$\mathrm{N_2$ + 3H_2 \rightarrow 2NH_3}. ($$Molar mass $$\mathrm{N_2$} = 28.0 g/$$mol, $$\mathrm{NH_3$} = 17.0 g/$$mol)

Accepted Answer

38.4 g

Question 7

Which of the following is NOT a requirement for a chemical reaction to occur?

Accepted Answer

Reactants must be in liquid form

Question 8

A catalyst affects a chemical reaction by:

Accepted Answer

Lowering the energy of activation

Question 9

If the concentration of one reactant is increased, what happens to the reaction rate?

Accepted Answer

It increases

Question 10

Which of the following is a correct multi-step plan for converting grams of $$\mathrm{Fe_2O_3} to $$grams of $$\mathrm{O_2$} in a $$reaction?

Accepted Answer

grams $$\mathrm{Fe_2O_3}$$ $$\rightarrow$$ moles $$\mathrm{Fe_2O_3}$$ $$\rightarrow$$ moles $$\mathrm{O_2$}$$ $$\rightarrow$$ grams $$\mathrm{O_2$}$$

Question 11

Which scenario best illustrates an endothermic reaction?

Accepted Answer

A reaction where heat is absorbed and the temperature of the surroundings decreases.

Question 12

A reaction flask is placed in ice. What is the effect on the reaction rate?

Accepted Answer

The rate decreases

Question 13

Which of the following statements about catalysts is correct?

Accepted Answer

A catalyst increases the rate of reaction and is not used up.

Question 14

Which of the following is true about the energy profile of an exothermic reaction?

Accepted Answer

The energy of the products is less than the energy of the reactants.

Question 15

Which step is NOT part of the mass calculation for a chemical reaction?

Accepted Answer

Convert grams of substance B directly to grams of substance A without using moles.

Question 16

Which of the following would DECREASE the rate of a chemical reaction?

Accepted Answer

Removing some of the reactants

Question 17

A reaction has a high activation energy. What effect does adding a catalyst have?

Accepted Answer

It lowers the activation energy.

Question 18

Which of the following is a real-world example of an exothermic reaction?

Accepted Answer

Combustion of gasoline in a car engine

Question 19

Which of the following is a correct statement about reaction rates?

Accepted Answer

Reaction rate increases with increasing concentration of reactants.

Chemical Quantities and Energy in Chemical Reactions

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