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.
Light a candle and hold a metal spoon over the flame.
What will happen to the wick?
Is this change reversible?
The wick burns and turns black and part of it turns to ash.
No, this is an irreversible change, because once the wick is burnt, it cannot be changed back to the original wick again.
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
When clear limewater is mixed with carbon dioxide, the reaction forms a substance called calcium carbonate.
1. Name the reactants in the reaction.
2. Name the products in the reaction.
Reactants:
Limewater
Carbon dioxide
Product:
Calcium carbonate
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
Does Sugar dissolve more quickly in hot or cold water?
Give a reason for your answer
Sugar dissolves more quickly in hot water.
Reason:
Hot water has more heat energy, so the water particles move faster. These fast-moving particles hit the sugar crystals more often and with more force, helping the sugar break down and mix into the water quickly.
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.
Ravi is adding copper sulfate to water and dissolving it.
Which substance is the solvent?
Which substance is the solute?
Solvent: Water
Solute: Copper sulfate
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.
Which process is faster: boiling or evaporation?
Why?
Boiling is faster
Happens at a fixed temperature (boiling point).
Bubbles are seen throughout the liquid.
The process is fast.
Heat is supplied continuously.
Evaporation
Happens at any temperature (not fixed).
Takes place only at the surface of the liquid.
The process is slow.
No bubbles are formed.