Energy Changes and Reversible Reactions

What is an endothermic reaction

• energy is absorbed

• energy is released

• energy is multiplied

• energy is destroyed

Tags

NGSS.HS-PS1-4

Calculate ΔH for the following reaction:

CH_{4 (g)} + O₂ (g) ⇌ CO_{2 (g)} + H₂O (l)

Compound ΔH

CH₄ (g) -74.8 kJ/mol

H₂O (l) -285.8 kJ/mol

CO₂ (g) -393.5 kJ/mol

• -604.5 kJ/mol

• -890.3 kJ/mol

• 890.3 kJ/mol

• 889.7 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

Which of the following correctly describes processes that happen during reactions?

• Bonds are broken in reactants, which is an exothermic process that takes in energy

• Bonds are broken in reactants, which is an endothermic process that gives out energy

• Bonds are made in products, which is an endothermic process that takes in energy

• Bonds are made in products, which is an exothermic process that gives out energy

Tags

NGSS.HS-PS1-4

The combustion of ethane (C₂H₆) is represented by the equation:

2C₂H₆(g) + 7O₂(g) 4CO₂(g) + 6H₂O(l)

• the rate of consumption of ethane is seven times faster than the rate of consumption of oxygen.

• the rate of formation of CO₂ equals the rate of formation of water.

• CO₂ is formed twice as fast as ethane is consumed.

• he rate of consumption of oxygen equals the rate of consumption of water.

Tags

NGSS.HS-PS1-5

The speed of a chemical reaction

• between ions in aqueous solution is extremely rapid because there are no bonds that need to be broken.

• is independent of the amount of contact surface of a solid involved.

• is constant no matter what the temperature is.

• varies inversely with the absolute temperature.

Tags

NGSS.HS-PS1-5

When the concentration of reactant molecules is increased, the rate of reaction increases. The best explanation is: As the reactant concentration increases,

• the activation energy increases.

• the rate constant increases.

• the average kinetic energy of molecules increases.

• the frequency of molecular collisions increases.

Tags

NGSS.HS-PS1-5

Magnesium needs to be heated before it reacts with oxygen in the air. What conclusion can you draw from this?

• The reaction is reversible

• The reaction has a high activation energy

• The reaction is exothermic

• Magnesium has a high melting point

Tags

NGSS.HS-PS1-5

Which of the following reactions releases most energy to the surroundings?

• Reaction energy change = -456 kJ/mol

• Reaction energy change = +547 kJ/mol

• Reaction energy change = +1456 kJ/mol

• Reaction energy change = -38 kJ/mol

Tags

NGSS.HS-PS1-4

The equations for three reactions are given below.

Reaction 1 H2 –> 2H

Reaction 2 HCl –> H + Cl

Reaction 3 2H + O –> H2O

Which reaction/s is/are exothermic?

• Reaction 3 only.

• Reaction 1 and 2 only.

• Reaction 1 and 3 only.

• Reaction 2 and 3 only.

Tags

NGSS.HS-PS1-4

The H-H bond energy is 436 kJ/mol and the Cl-Cl bond energy is 242 kJ/mol.

What is the H-Cl bond energy?

• 247 kJ

• 431 kJ

• 494 kJ

• 862 kJ

Tags

NGSS.HS-PS1-4