Q: If a chemical reaction requires $2$ moles of a substance, how many molecules are needed? (Use Avogadro's number: $6.022 \times 10^{23}$)

$1.2044 \times 10^{24}$ molecules

Question 1

Which of the following is an example of a quantitative observation in a laboratory experiment?

Accepted Answer

The temperature increased by 5 degrees Celsius.

Question 2

Convert $0.000789$ to scientific notation with three significant figures.

Accepted Answer

$7.89 	imes 10^{-4}$

Question 3

If a chemical reaction requires $2$ moles of a substance, how many molecules are needed? (Use Avogadro's number: $6.022 	imes 10^{23}$)

Accepted Answer

$1.2044 	imes 10^{24}$ molecules

Question 4

A scientist needs to express a measurement of $0.0000000075$ meters using a metric prefix. Which is the most appropriate expression?

Accepted Answer

$7.5$\,nanometers

Question 5

How many significant figures are in the number $0.0200$?

Accepted Answer

3

Question 6

If you multiply $2.5$ by $3.42$, how many significant figures should the result have?

Accepted Answer

2

Question 7

Calculate the following expression and express the answer with the correct number of significant figures: $$(6.022 	imes 10^{23}) 	imes \left(\frac{3.0}{2.5}ight) + 1.2$$

Accepted Answer

$7.2 	imes 10^{23}$

Question 8

A car's fuel efficiency is rated at $25$ miles per gallon. If $1$ gallon equals $3.785$ liters and $1$ mile equals $1.60934$ km, how many kilometers per liter does the car achieve?

Accepted Answer

$10.6$ km/L

Question 9

Convert $45.0$ grams to ounces using the conversion factor $1$ ounce $= 28.3495$ grams. What is the result with the correct significant figures?

Accepted Answer

$1.59$ ounces

Question 10

Convert a density of $1.5$ g/cm$^3$ to kg/m$^3$.

Accepted Answer

$1500$ kg/m$^3$

Question 11

A metal object is submerged in a graduated cylinder, causing the water level to rise from $30.0$ mL to $36.5$ mL. If another object is added and the water level rises to $42.0$ mL, what is the volume of the second object?

Accepted Answer

$5.5$ mL

Question 12

Which of the following best describes a compound?

Accepted Answer

A substance made of two or more different elements chemically bonded

Question 13

Why is diamond considered one of the hardest materials?

Accepted Answer

Due to its strong covalent bonds and rigid lattice structure.

Question 14

Which phase change involves a substance going directly from a solid to a gas?

Accepted Answer

Sublimation

Question 15

How are reactants transformed into products during a chemical reaction?

Accepted Answer

Through a chemical change that breaks and forms new bonds.

Question 16

A cylinder has a radius of $2$ cm and a height of $5$ cm. What is its volume?

Accepted Answer

$62.8$\,cm^3$

Question 17

Which of the following best defines thermal energy?

Accepted Answer

The sum of the kinetic and potential energies of all atoms in an object.

Question 18

In a closed system, $10$ grams of $A$ reacts with $15$ grams of $B$ to form $5$ grams of $C$ and an unknown amount of $D$. What is the mass of $D$?

Accepted Answer

$20$ grams

Question 19

How many joules are in $2$ kilowatt hours?

Accepted Answer

$7.2 	imes 10^{6}$\,joules

Question 20

A system absorbs $50$ J of heat and does $20$ J of work on its surroundings. What is the change in internal energy ($\Delta U$)?

Accepted Answer

$30$ J

Question 21

In an energy diagram for an endothermic reaction, how do the energy levels of reactants and products compare?

Accepted Answer

Reactants have lower energy than products.

Question 22

If $400$ J of heat is applied to $3$ moles of a substance, resulting in a temperature change of $10^{\circ}$C, what is the molar heat capacity?

Accepted Answer

$13.33$\,J/mol^{\circ}$C

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