Energetics Lecture 1 Review

Chemical Energetics Lecture 1 Review

Multiple Choice

Which type of reaction does the graph represent?

• Endothermic reaction

• Exothermic reaction

Multiple Choice

Endothermic reactions have ___________ enthalpy change because heat energy is added to the reaction.

• negative

• zero

• positive

Multiple Choice

Exothermic reactions are ones that _______

• release energy to the surroundings

• absorb energy from the surroundings

• remain at a constant temperature

• decrease in temperature

Multiple Choice

Given the following reaction and its enthalpy change,
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ \ \ \ \ \ \ \Delta H\ =\ -393\ kJ$   

what is the enthalpy change of the following reaction?
 $2C\ \left(s\right)\ +\ 2O_2\left(g\right)\ \rightarrow\ 2CO_{2\ }\left(g\right)\$ 

•  $\frac{-393}{2}kJ$  

• -393 kJ

• 2(-393) kJ

• + 393 kJ

Multiple Choice

Given the following reaction and its enthalpy change,
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ \ \ \ \ \ \ \Delta H\ =\ -393\ kJ$   

what is the enthalpy change of the following reaction?
 $\frac{1}{2}C\ \left(s\right)\ +\ \frac{1}{2}O_2\left(g\right)\ \rightarrow\ \frac{1}{2}CO_{2\ }\left(g\right)\$  

•  $\frac{-393}{2}kJ$  

• -393 kJ

• 2(-393) kJ

• + 393 kJ

Multiple Choice

Given the following reaction and its enthalpy change,
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ \ \ \ \ \ \ \Delta H\ =\ -393\ kJ$   

what is the enthalpy change of the following reaction?
 $CO_2\left(g\right)\ \rightarrow\ C\left(s\right)\ +\ O_2\left(g\right)$  

•  $\frac{-393}{2}kJ$  

• -393 kJ

• 2(-393) kJ

• + 393 kJ

Multiple Choice

Given the following reaction and its enthalpy change,
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ \ \ \ \ \ \ \Delta H\ =\ -393\ kJ$   

what is the enthalpy change of the following reaction?
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ +\ N_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ +\ N_2\left(g\right)\ \$  

•  $\frac{-393}{2}kJ$  

• -393 kJ

• 2(-393) kJ

• + 393 kJ

Quick check

In the previous question,
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ +\ N_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)\ +\ N_2\left(g\right)\$  
  
simplifies to 
 $C\ \left(s\right)\ +\ O_2\left(g\right)\ \rightarrow\ CO_{2\ }\left(g\right)$  

The enthalpy change of the net equation is -393 kJ.

Multiple Choice

Enthalpy change of formation is the enthalpy change when _________

• 1 mole of reactant is used

• 1 mole of product is formed from its atoms in gaseous state

• 1 mole of product is formed from its elements in standard states

• 1 mole of element is used

Definition:

Enthalpy change of formation is the enthalpy change when 1 mole of substance is formed from its constituent elements in their standard states.

Multiple Choice

Which equation represents enthalpy change of formation of sodium chloride?

• Na(g) + Cl(g)

  → NaCl(g)

• Na(s) + Cl(g)

  → NaCl(s)

• Na(s) + ½ Cl₂(g)

  → NaCl(s)

• 2Na(s) + Cl₂(g)

  → 2NaCl(s)

Multiple Choice

What are the coefficients of the equation for enthalpy change of formation of aluminium oxide?

_ Al (s) + _ $O_2\left(g\right)\rightarrow$  _  $Al_2O_3\ \left(s\right)$  

• 2, 3, 1

• 2,  $\frac{3}{2}$  , 1

• 4, 3, 2

• 1, 1, 2

Multiple Choice

What are the coefficients of the equation for enthalpy change of formation of ethane?

_ C (s) + _ $H_2\left(g\right)\rightarrow$  _  $C_2H_6\ \left(g\right)$  

•  $1,\ \frac{3}{2},\ \frac{1}{2}$  

• 1, 2, 3

• 2, 3, 1

• 2, 6, 1

Multiple Choice

Enthalpy change of combustion is the heat energy evolved when one mole of

• carbon dioxide is formed

• substance is burnt in limited oxygen

• substance is completely burnt in excess oxygen

• water is formed

Standard enthalpy change of combustion is the the heat energy evolved when 1 mole of substance is completely burnt in excess oxygen at 298K and 1 bar.

Note: 

 $\Delta H_c$  is always exothermic.

Multiple Choice

What are the coefficients of the equation for enthalpy change of combustion of ethane?

 $..C_2H_6\left(g\right)\ +..O_2\left(g\right)\ \rightarrow\ ..CO_2\left(g\right)\ +\ ..H_2O\left(l\right)$  

•  $1,\ \frac{7}{2},\ 2,\ 3$  

• 1, 5, 2, 3

• 1, 7, 2, 3

• 2, 7, 4, 6