Properties of substances
Ice melts at a temperature of _________
0 °C
Heat cannot be transferred from one object to another.
True or False
False.
Dissolving sugar in water → Reversible or Irreversible?
Reversible
Give one example for chemical reaction
Learners response
(some examples)
Burning of paper/wood – produces ash, smoke, and gases.
Rusting of iron – iron reacts with oxygen and moisture to form rust.
Cooking food – new substances are formed while heating.
Digesting food – food is broken down into simpler substances in the stomach.
Baking a cake – ingredients react and change into a fluffy cake.
Souring of milk – milk turns into curd/yogurt.
Which process is faster: boiling or evaporation?
Why?
Happens at a fixed temperature (boiling point).
Bubbles are seen throughout the liquid.
The process is fast.
Heat is supplied continuously.
Happens at any temperature (not fixed).
Takes place only at the surface of the liquid.
The process is slow.
No bubbles are formed.
When a liquid boils, all the particles in the liquid have enough energy to become a gas.
True or False
True
Substances and materials that conduct heat well are called _______________
Thermal conductors
Burning paper → Reversible or Irreversible?
Irreversible
When some substances are mixed together, they change and form a new substance. This is called a _______________
Chemical reaction
Which among the following is not a property of a gas?
a) It takes up space
b) It is packed tightly
c) It has mass
(b) It is packed tightly
Give one example of a poor conductor of heat.
wood, plastic, rubber, glass, wool, air, cork
If you accidentally spill salt in water, is this change reversible or irreversible?
Reversible
Choose the correct answer
The substances that react together are called _________. The new substances that form are called the ___________.
1. products and reactants
2. reactions and reacts
3. reactants and products
3. reactants and products
Evaporation can occur at any temperature.
Do you agree or disagree?
Answer: Agree
Evaporation can take place at any temperature, because particles at the surface of a liquid can escape into the air if they gain enough energy.
Find out the name for materials and substances that are not good conductors of heat.
Insulators
Why is the melting of ice considered a reversible change, but burning paper is irreversible?
Melting of ice is reversible because water can freeze back into ice.
Burning paper is irreversible because it turns into ash and cannot return to paper
Sana drops a fizzy tablet into a glass of water. What evidence will she have that a chemical reaction is taking place?
She will see bubbles/fizzing because a gas is produced.
Change in sound (fizzing).
The tablet disappears as new substances form.
Which of the following substances has a melting point of about 1064 °C?
a) Gold
b) Liquid gold
c) Vinegar
a) Gold
In which cup will your tea stay warm longest:
A) a stainless steel cup
B) a glass cup
C) a polystyrene foam cup
Give one reason
c)a polystyrene foam cup
Reason: very poor conductor of heat and keeps the heat inside.
When we mix boiling water with jelly powder it becomes a liquid. In the fridge it becomes a solid. How can we make solid jelly change back to a liquid?
Reheat it
When vinegar and baking soda react, we can see that gas is produced. How can we tell that a reaction has taken place?
1. A new substance (carbon dioxide gas) is formed.
2. There is fizzing/bubbling when the gas is released.