Chemical Reactions and Enthalpy Changes

This video tutorial covers the topic of energetics in IGCSE and GCSE chemistry. It explains key concepts such as endothermic and exothermic reactions, energy profiles, and activation energy. The video also includes example questions to demonstrate how these concepts are tested in exams. Additionally, it covers calculations related to heat energy changes, combustion, and bond energies. Practical experiments are analyzed to understand the effects of different variables on temperature changes.

What is a characteristic of an endothermic reaction?

• The temperature of the surroundings increases.

• More energy is needed to make bonds than to break them.

• The change in energy is negative.

• Heat energy is released.

Which of the following is an example of an exothermic reaction?

• Evaporation

• Melting ice

• Combustion

• Photosynthesis

What does the activation energy represent in a chemical reaction?

• The energy required to start a reaction

• The energy difference between reactants and products

• The total energy released by the reaction

• The energy absorbed by the surroundings

How do catalysts affect a chemical reaction?

• They increase the activation energy.

• They are consumed in the reaction.

• They decrease the energy of the reactants.

• They provide an alternative pathway with lower activation energy.

What is the temperature change when lithium iodide dissolves in water if the initial temperature is 16.7°C and the final temperature is 22.3°C?

• 4.9°C

• 6.0°C

• 7.2°C

• 5.6°C

In the combustion of methane, what is a likely reason for a lower experimental molar enthalpy change compared to the data book value?

• Incorrect measurement of gas volume.

• Methane is not pure.

• Incomplete combustion.

• Heat loss to the surroundings.

What is the molar enthalpy change for the combustion of methane if 29,200 J of energy is released and 0.0604 moles of methane are burned?

• 483 kJ/mol

• 510 kJ/mol

• 698 kJ/mol

• 890 kJ/mol

What effect does increasing the distance between the spirit burner and the copper can have on the maximum temperature reached?

• Increases the temperature

• Decreases the temperature

• No effect on temperature

• Causes temperature to fluctuate

How is the molar enthalpy change calculated in the pentane combustion experiment?

• Energy divided by number of moles

• Energy divided by volume

• Energy divided by mass

• Energy multiplied by number of moles

What is the calculated molar enthalpy change for the combustion of pentane if 51,900 J of energy is released and 1.88 grams of pentane are burned?

• 1850 kJ/mol

• 2100 kJ/mol

• 2200 kJ/mol

• 1990 kJ/mol