Conditions on the arrow

The idea

Reaction conditions such as temperature, pressure or a catalyst are sometimes written above and/or below the arrow of a chemical equation.

A recipe card

A recipe says: mix flour and water, bake at 180 °C. The temperature is not an ingredient: it is a condition. A chemical equation can say the same.

Where in an equation would such a condition be written?

• On the arrow, above and/or below it
• Instead of a formula
• On the right, after the products

Write the conditions

Tap a tile, then tap the empty space above or below the arrow.

Above and below the arrow

Reaction conditions such as temperature, pressure or a catalyst are sometimes written above and/or below the arrow of a chemical equation.

• Reaction | On the arrow
• CO(g) + 2H₂(g) → CH₃OH(l) | 340 atm (pressure)
• 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O | Sunlight, Chlorophyll

Notes

Reaction conditions such as temperature, pressure or a catalyst are sometimes written above and/or below the arrow of a chemical equation.

Check yourself

Which of these is NOT written on the arrow?

In the photosynthesis equation, what is written on the arrow?

Why do we write 340 atm on the arrow of CO(g) + 2H₂(g) → CH₃OH(l)?

• Pressure. Pressure can be written on the arrow, like 340 atm.
• A catalyst. A catalyst can be written on the arrow.
• The product — correct. Yes! Products go on the RHS, after the arrow.
• Sunlight and chlorophyll — correct. Yes! They are the conditions for the reaction.
• Glucose and oxygen. These are products. They are written after the arrow.
• Carbon dioxide and water. These are reactants, written before the arrow.
• It is the mass of the product. atm is a unit of pressure, not mass.
• It shows the pressure at which the reaction takes place — correct. Yes! It is a reaction condition.
• It is the coefficient of CO. Coefficients are written in front of formulae, not on the arrow.