# Reading equations: states and conditions

> What the brackets and the arrow tell you


## Objectives

- Read the state symbols (s), (l), (g), (v) and (aq).
- Read what is written over the arrow: heat (Δ), temperature, pressure, catalyst.
- Tell reactants and products apart from the conditions.

## 1. Magnetic properties and catalytic activity




## 2. What does 500 °C mean?

Predict: what does 500 °C over the arrow tell you?

- 500 °C is one of the products
- The reaction needs a temperature of 500 °C ✓
- The reaction gives out 500 °C of heat

500 °C over the arrow is a condition: the reaction needs this temperature to take place. Products are written after the arrow as formulas, and a temperature is not a substance.

[ar-EG] الـ 500 °C اللي فوق السهم دي condition: يعني الـ reaction محتاجة درجة الحرارة دي عشان تحصل. أما الـ products فبتتكتب بعد السهم على هيئة formulas، والـ temperature مش مادة.
## 3. State symbols

State symbol A letter in brackets after a formula that shows the physical state of the substance. Read it: solid zinc and hydrochloric acid solution give zinc chloride solution and hydrogen gas.


## 4. Over the arrow

Over and under the arrow go the **conditions**: Δ (heating), a temperature, a pressure or a catalyst. $\ce{MnO2}$ is a reactant in this reaction.


## 5. Read new equations

Sort each part of this equation: In this reaction, the $\ce{CO2}$ comes off as a ___, and the $\ce{CaCl2}$ is ___ in water.


## 6. Summary

(s) solid, (l) liquid, (g) gas, (v) vapour, (aq) dissolved in water. Over the arrow: conditions: Δ (heat), temperature, pressure, catalyst. What is over the arrow is neither a reactant nor a product. The Haber-Bosch method writes 500 °C, 200 atm and Fe over its arrow. Can you explain why a catalyst is written over the arrow and not with the reactants? A catalyst such as $\ce{MnO2}$ is a condition: it is not used up, so it is on neither side. It is written over the arrow.



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-chem.equation-reading