<< Chapter < Page Chapter >> Page >

State symbols and other information

The state (phase) of the compounds can be expressed in the chemical equation. This is done by placing the correct label on the right hand side of the formula. There are only four labels that can be used:

  1. (g) for gaseous compounds
  2. (l) for liquids
  3. (s) for solid compounds
  4. (aq) for an aqueous (water) solution

To show that heat is needed for a reaction, a Greek delta ( Δ ) is placed above the arrow.

You may remember from Physical and chemical change that energy cannot be created or destroyed during a chemical reaction but it may change form. In an exothermic reaction, Δ H is less than zero and in an endothermic reaction, Δ H is greater than zero. This value is often written at the end of a chemical equation.

Solid zinc metal reacts with aqueous hydrochloric acid to form an aqueous solution of zinc chloride ( ZnCl 2 )and hydrogen gas. Write a balanced equation for this reaction.

  1. The reactants are zinc ( Zn ) and hydrochloric acid ( HCl ). The products are zinc chloride ( ZnCl 2 ) and hydrogen ( H 2 ).

  2. Zn + HCl ZnCl 2 + H 2
  3. You will notice that the zinc atoms balance but the chlorine and hydrogen atoms don't. Since there are two chlorine atoms on the right and only one on the left, we will give HCl a coefficient of 2 so that there will be two chlorine atoms on each side of the equation.

    Zn + 2 HCl ZnCl 2 + H 2

  4. When you look at the equation again, you will see that all the atoms are now balanced.

  5. In the initial description, you were told that zinc was a metal, hydrochloric acid and zinc chloride were in aqueous solutions and hydrogen was a gas.

    Zn ( s ) + 2 HCl ( aq ) ZnCl 2 ( aq ) + H 2 ( g )

Balance the following equation:

( NH 4 ) 2 SO 4 + NaOH NH 3 + H 2 O + Na 2 SO 4

In this example, the first two steps are not necessary because the reactants and products have already been given.

  1. With a complex equation, it is always best to start with atoms that appear only once on each side i.e. Na , N and S atoms. Since the S atoms already balance, we will start with Na and N atoms. There are two Na atoms on the right and one on the left. We will add a second Na atom by giving NaOH a coefficient of two. There are two N atoms on the left and one on the right. To balance the N atoms, NH 3 will be given a coefficient of two. The equation now looks as follows:

    ( NH 4 ) 2 SO 4 + 2 NaOH 2 NH 3 + H 2 O + Na 2 SO 4

  2. N , Na and S atoms balance, but O and H atoms do not. There are six O atoms and ten H atoms on the left, and five O atoms and eight H atoms on the right. We need to add one O atom and two H atoms on the right to balance the equation. This is done by adding another H 2 O molecule on the right hand side. We now need to check the equation again:

    ( NH 4 ) 2 SO 4 + 2 NaOH 2 NH 3 + 2 H 2 O + Na 2 SO 4

    The equation is now balanced.

The following video explains some of the concepts of balancing chemical equations.

Khan academy video on balancing chemical equations

Questions & Answers

I'm interested in biological psychology and cognitive psychology
Tanya Reply
what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Siyavula textbooks: grade 10 physical science [caps]. OpenStax CNX. Sep 30, 2011 Download for free at http://cnx.org/content/col11305/1.7
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 10 physical science [caps]' conversation and receive update notifications?

Ask