A student is investigating chemical reactions that produce heat.
She adds magnesium ribbon to hydrochloric acid, HCl\text{HCl}HCl.
Magnesium chloride, MgCl2\text{MgCl}_2MgCl2, and hydrogen gas are made.
Write the balanced symbol equation for this reaction.
What term is used to describe a reaction that releases heat to the surroundings?
Explain what is meant by the term activation energy.
Combustion reactions produce a lot of heat energy. Bond energies can be used to calculate the energy change in reactions.
| Bond | Bond energy (kJ/mol) |
|---|---|
| H−H\text{H}-\text{H}H−H | 436 |
| O=O\text{O}=\text{O}O=O | 498 |
| O−H\text{O}-\text{H}O−H | 464 |
Hydrogen reacts with oxygen to produce water as shown:
2H−H+O=O⟶2H−O−H2\text{H}-\text{H} + \text{O}=\text{O} \longrightarrow 2\text{H}-\text{O}-\text{H}2H−H+O=O⟶2H−O−H
The reaction of hydrogen with oxygen produces heat. Explain why. Use ideas about bond breaking and bond making in your answer.
Calculate the total energy transferred to break the bonds in the reactants.
Calculate the total energy transferred to make the bonds in the products.
Use your answers to parts (ii) and (iii) to calculate the energy change for the reaction.