[C5] Energy changes

What is the conservation of energy law?

Energy cannot be created or destroyed, it can only be transferred

What is an exothermic reaction?

A reaction that transfers energy to the surroundings

What is an endothermic reaction?

A reaction that takes in energy from the surroundings

What happens to the temperature of the surroundings in an exothermic reaction?

The temperature increases

What happens to the temperature of the surroundings in an endothermic reaction?

The temperature decreases

What happens to the energy of the reactants in exothermic reactions?

The reactants lose energy to form the products

What happens to the energy of the reactants in endothermic reactions?

The reactants gain energy to form the products

What are examples of exothermic reactions?

combustion, many oxidation reactions and neutralisation

What type of reaction are combustion reactions?

exothermic

What type of reaction are neutralisation reactions?

exothermic

What type of reaction are most oxidation reactions?

exothermic

What type of reaction takes place in hand warmers?

exothermic

What type of reaction takes place in self heating cans

exothermic

What type of reaction are thermal decomposition reactions?

endothermic

What is a thermal decomposition reaction?

The breakdown of a substance on heating

What type of reaction occurs when citric acid reacts with sodium hydrogencarbonate?

endothermic

What is the activation energy?

The minimum amount of energy required for a reaction to occur

What distance is labelled the activation energy on reaction profiles?

The distance from the reactants to the top of the peak

What is the overall energy change?

The difference in energy between the reactants and products

What type of reaction takes place in sports injury packs?

endothermic

𝙒𝙝𝙚𝙣 𝙞𝙣𝙫𝙚𝙨𝙩𝙞𝙜𝙖𝙩𝙞𝙣𝙜 𝙚𝙭𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙖𝙣𝙙 𝙚𝙣𝙙𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨: Why should you carry out the investigation in a polystyrene cup?

To prevent energy being transferred to and from the surroundings (makes the results more accurate)

𝙒𝙝𝙚𝙣 𝙞𝙣𝙫𝙚𝙨𝙩𝙞𝙜𝙖𝙩𝙞𝙣𝙜 𝙚𝙭𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙖𝙣𝙙 𝙚𝙣𝙙𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨: Why should you use a lid?

To prevent energy being transferred to and from the surroundings (makes the results more accurate)

𝙒𝙝𝙚𝙣 𝙞𝙣𝙫𝙚𝙨𝙩𝙞𝙜𝙖𝙩𝙞𝙣𝙜 𝙚𝙭𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙖𝙣𝙙 𝙚𝙣𝙙𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨: Why should you place the polystyrene cup in a beaker?

To prevent the cup from falling over

𝙒𝙝𝙚𝙣 𝙞𝙣𝙫𝙚𝙨𝙩𝙞𝙜𝙖𝙩𝙞𝙣𝙜 𝙚𝙭𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙖𝙣𝙙 𝙚𝙣𝙙𝙤𝙩𝙝𝙚𝙧𝙢𝙞𝙘 𝙧𝙚𝙖𝙘𝙩𝙞𝙤𝙣𝙨: Why should you stir the solution after adding the sodium hydroxide?

To spread the thermal energy out through the solution

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of process is bond breaking?

Endothermic

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of process is bond making?

Exothermic

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What are the units for overall energy change?

kJ/mol

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of reaction has a negative value for overall energy change?

exothermic

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What type of reaction has a positive value for overall energy change?

endothermic

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] What is the equation used to calculate overall energy change?

overall energy change = energy required to break bonds - energy released when new bonds are formed

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] How does the energy needed to break bonds compare with the energy released when new bonds are formed in exothermic reactions?

The energy released when new bonds are formed is greater than the energy needed to break exisiting bonds

[𝗛𝗶𝗴𝗵𝗲𝗿 𝘁𝗶𝗲𝗿] How does the energy needed to break bonds compare with the energy released when new bonds are formed in endothermic reactions?

The energy needed to break existing bonds is greater than the energy released when new bonds are formed

How are batteries formed?

Two or more cells are connected together in series

What are chemical cells?

A store of internal energy that can be transferred as an electric current in a circuit

What does the voltage of a cell depend on?

What the electrodes are made from and the substance used as the electrolyte

What type of batteries are non-rechargeable?

Alkaline batteries

How do rechargeable batteries work?

The chemical reactions are reversed when an external electrical current is supplied

What are fuel cells?

Cells that continuously produce a voltage when supplied with fuel and oxygen

What is the most expensive type of cell to manufacture?

Hydrogen fuel cells

What is the cheapest type of cell to manufacture?

Alkaline cells

What is a risk from using hydrogen fuel cell?

Hydrogen is very flammable